Systems and methods for managing noise in compact high speed and high force hydraulic actuators

ABSTRACT

Presented herein are systems and methods for attenuating certain pulsations in a hydraulic system comprising a pump and a hydraulic actuator. In certain aspects, an accumulator comprising an internal volume that is divided into a working chamber and a contained chamber may be utilized to at least partially attenuate propagation of certain pulsations in the system. The working chamber may be fluidically coupled to the pump via a first flow path and fluidically coupled to a chamber of the actuator via a second flow path. The system may be designed such that a first inertance of the first flow path is greater than a second inertance of the second flow path. Additionally or alternatively, the system may be designed such that a resonance associated with the first inertance and a compliance of the accumulator may occur at a resonance frequency of less than 90 Hz.

RELATED APPLICATIONS

This Application is a national stage filing under 35 U.S.C. 371 ofInternational Patent Application Serial No. PCT/US2017/035558, filedJun. 1, 2017, which claims the benefit of priority under 35 U.S.C. §119(e) of U.S. Provisional Application Ser. No. 62/344,571, filed Jun.2, 2016, the disclosures of each of which are incorporated herein byreference in their entirety.

BACKGROUND

Hydraulic systems, which take advantage of fluids to store, convert,and/or transport power, are utilized across a variety of industries andapplications, from large scale chemical plants to motor vehicles.Hydraulic systems generally include a variety of components, such as,for example, pumps, valves, various reservoirs, tanks, or fluidchambers, filters, membranes, loads, etc. Each component of a hydraulicsystem may be connected by flow-coupling elements such as pipes, tubes,nipples, hoses, channels, etc. of varying diameters and geometries. Inparticular, hydraulic systems that incorporate one or more hydraulicactuators have been investigated for use in a variety of applications,including automotive applications.

One phenomenon associated with hydraulic systems, especially forautomotive applications, is undesirable vibrations such as, for example,vibrations that result in acoustic noise. Acoustic noise may beintroduced into a hydraulic system via, for example, pulsations in inputflow and/or output flow generated by use of a positive displacementpump—a phenomenon known in the art as “pump ripple.” Alternatively,pulsations may be introduced by opening or closing of valves, therebytemporarily disrupting steady-state conditions in the hydraulic system,a phenomenon sometimes referred to in the art as “water hammer”(notably, despite the term “water hammer”, the phenomenon is not limitedto water-based systems and may involve any hydraulic fluid).

SUMMARY

Inventors have recognized that the practical use of hydraulic systemsmay be governed by several application dependent considerations, such asmaximum allowable noise specifications, space constraints, power orforce demands, and response time requirements. Often times, theseconsiderations may represent trade-offs; for example, adding componentssuch as noise absorbers may serve to mitigate acoustic noise, but mayadd bulk to the system and/or increase response time, thereby precludingcertain applications in which space is highly limited and/or very fastresponse times are desired. Accordingly, the Inventors have recognized atechnical need for hydraulic systems having an arrangement of hydrauliccomponents that serves to limit noise while having sufficient responsetime and compactness that allow for use in, for example, automotivesuspension applications.

The inventors have also recognized that the specific arrangement ofhydraulic components in a hydraulic system can have important effects onnoise, response time, and packaging size associated with the hydraulicsystem, often in ways that are not readily predictable using a-prioriinformation. Presented herein are various hydraulic systems, and methodsof use thereof, that may allow for one or more of low noise, fastresponse-time operation, while permitting flexibility and compactness inpackaging. Though the various embodiments described herein should not belimited to providing these exemplary benefits and other possiblebenefits are also possible.

In one aspect, a hydraulic apparatus is disclosed comprising: ahydraulic actuator including an actuator housing that at least partiallydefines a compression chamber and an extension chamber and a pump (e.g.,a hydraulic pump, a hydraulic motor capable of operating as a pump, abidirectional pump, a bidirectional positive displacement pump); acompression-side accumulator comprising a compression-side accumulatorhousing defining a first internal volume that is divided, by a firstbarrier (e.g., a movable barrier (e.g., a slidable piston, a bladder orportion thereof)), into a first contained chamber (e.g., a chambercontaining a compressible fluid (e.g., a gas)) and a first workingchamber, wherein the first working chamber is fluidically coupled to thepump by a compression-side first flow path and the first working chamberis fluidically coupled to the pump by a compression-side second flowpath.

In certain embodiments of the hydraulic apparatus, a firsthydropneumatic system consisting of the compression-side first flow pathand the compression-side accumulator has a first resonance frequencythat is less than 90 Hz. In certain embodiments, the first resonancefrequency may be less than 50 Hz, or less than 20 Hz. In certainembodiments, the first resonance frequency is greater than 1 Hz. Incertain embodiments, the compression-side first flow path has a firstend in the pump and a second end in the first working chamber. Incertain embodiments, the compression-side first flow path has exactlytwo ends.

In certain embodiments of the hydraulic apparatus, a secondhydropneumatic system consisting of the compression-side second flowpath and the compression-side accumulator has a second resonancefrequency that is greater than the first resonance frequency (e.g., by afactor of at least 5 or at least 20). In certain embodiments, the thirdfrequency is less than 1000 Hz and/or greater than 500 Hz.

In certain embodiments, the hydraulic apparatus further comprises anextension flow path that fluidically couples the pump to the extensionchamber of the actuator, and an extension side accumulator comprising anextension-side accumulator housing defining a second internal volumethat is divided, by a second barrier (e.g., a movable barrier (e.g., aslidable piston, a bladder or portion thereof)), into a second containedchamber (e.g., a chamber containing a compressible fluid (e.g., a gas))and a second working chamber. In certain embodiments, the extension-sideaccumulator has a second stiffness and the compression-side accumulatorhas a first stiffness, and the second stiffness is greater than thefirst stiffness (e.g., by a factor of at least 2, by a factor of atleast 5, by a factor not exceeding 100).

In certain embodiments, the compression-side accumulator is a type-2accumulator. In certain embodiments, the extension-side accumulator is atype-1 accumulator. In certain embodiments, the extension-sideaccumulator further comprises a cylindrical neck (e.g., a neck having adiameter between 4-10 mm, and/or a length less than 5 mm) thatfluidically couples the second working chamber to the extension flowpath. In certain embodiments, the second barrier comprises a firstsurface exposed to fluid in the working chamber, and wherein across-sectional area of the neck is less than the surface area of thefirst surface.

In another aspect, a hydraulic actuator is disclosed comprising anactuator housing that at least partially defines a compression chamberand an extension chamber; a pump (e.g., a hydraulic motor capable ofoperating as a pump, a bidirectional pump, a bidirectional positivedisplacement pump); a compression-side accumulator comprising: acompression-side accumulator housing defining a first internal volumethat is divided, by a first barrier (e.g., a movable barrier (e.g., aslidable piston, a bladder or portion thereof)), into a first containedchamber (e.g., a chamber containing a compressible fluid (e.g., a gas))and a first working chamber, wherein: the first working chamber isfluidically coupled to the pump by a compression-side first flow path;and the first working chamber is fluidically coupled to the compressionchamber by a compression-side second flow path.

In certain embodiments, the compression-side first flow path has a firstinertance and the compression-side second flow path has a secondinertance, and the first inertance is larger than the second inertance.For example, the first inertance may be greater than the secondinertance by a factor of at least 5 or at least 10. In certainembodiments, the first inertance is greater than the second inertance bya factor of no more than 100.

Alternatively or additionally, in certain embodiments at least one of(a) and (b) as follows is true: (a) a first TFmag of a first transferfunction has at least one of a first global maximum and first localmaximum at a first frequency, and a second TFmag of a second transferfunction has at least one of a second global maximum and second localmaximum at a second frequency, wherein: the first transfer functiondescribes a first relationship between pressure at a first point andpressure at a second point; the second transfer function describes asecond relationship between pressure at the second point and pressure ata third point; the first point is located in one of: the pump, a port ofthe pump, and the compression-side first flow path; the second point islocated in the first internal volume (e.g., inside the first workingchamber) of the compression-side accumulator; and the third point islocated in the compression chamber of the actuator; and (b) a first TFphof a first transfer function is equal to +/−90° at a first frequency,and a second TFph of a second transfer function is equal to +/−90° at asecond frequency; wherein the first transfer function describes a firstrelationship between pressure at a first point and pressure at a secondpoint; the second transfer function describes a second relationshipbetween pressure at the second point and pressure at a third point inthe first point is located in one of: the pump, port and thecompression-side first flow path; the first point is located in one of:the pump, a port of the pump, and the compression-side first flow path;the second point is located in the first internal volume (e.g., insidethe first working chamber) of the compression-side accumulator; thethird point is located in the compression chamber of the actuator. Incertain embodiments, (a) as listed above is true. In certainembodiments, (b) as listed above is true. In certain embodiments, both(a) and (b) are true.

In certain embodiments, the second frequency is higher than the firstfrequency. For example, the second frequency may be greater than thefirst frequency by a factor of at least 5 or at least 20. In certainembodiments, the second frequency may be greater than the firstfrequency by a factor of less than 100. In certain embodiments, thefirst frequency is higher than a first lower limit and lower than afirst upper limit, wherein the first lower limit is one of 0 Hz, 2 Hz, 5Hz, or 10 Hz and the first upper limit is one of 100 Hz, 80 Hz, 60 Hz,50 Hz, 30 Hz, 20 Hz, or 15 Hz. In certain embodiments, the secondfrequency is higher than a second lower limit and lower than a secondupper limit, wherein the second lower limit is one of 100 Hz, 200 Hz,300 Hz, 400 Hz, or 500 Hz and the second upper limit is one of 800 Hz,1000 Hz, or 1500 Hz.

In certain embodiments, the compression-side first flow path has a firstlength and the compression-side second flow path has a second length,and the first length is longer than the second length. For example, thefirst length may be equal to at least 2 times or at least 5 times thesecond length. In certain embodiments, the first length is greater thanthe second length by a factor of no more than 50.

In certain embodiments, compression-side first flow path comprises afirst portion having a first cross-sectional area and thecompression-side second flow path comprises a second portion having asecond cross-sectional area, and the first cross-sectional area islarger than the second cross-sectional area (e.g., by a factor of atleast 2 or at least 5, and/or by a factor of less than 100).

In certain embodiments, the actuator further comprises an actuatorpiston having a first face at least partially exposed to fluid in theextension chamber and a second face at least partially exposed to fluidin the compression chamber. In certain embodiments, a piston rod may bephysically attached to the piston (e.g., the piston rod may bephysically attached to the first face of the piston).

In certain embodiments, the compression-side first flow path has a firstlength that is less than the length of the compression flow path. Incertain embodiments, the compression-side second flow path has a secondlength that is less than a length of the compression flow path. Incertain embodiments, the sum of the first length and the second lengthis less than the length of the compression flow path. In certainembodiments, the compression flow path is the shortest flow path of afirst set of one or more flow paths, the compression-side first flowpath is the shortest flow path of a second set of one or more flowpaths, and the compression-side second flow path is the shortest flowpath of a third set of one or more flow paths, wherein” the first set ofone or more flow paths consists of each flow path of the hydraulicapparatus that fluidically couples the pump to the compression chamber;the second set of one or more flow paths consists of each flow path ofthe hydraulic apparatus that fluidically couples the pump to the firstworking chamber; and the third set of one or more flow paths consists ofeach flow path of the hydraulic apparatus that fluidically couples thefirst working chamber to the compression chamber.

In certain embodiments, the compression-side accumulator is a type-2accumulator. In certain embodiments, the compression-side accumulatorcomprises a first opening through the compression-side accumulatorhousing; a second opening through the compression-side accumulatorhousing; and an internal flow path fluidically coupling the firstopening to the second opening, wherein the internal flow path isentirely contained in the first working chamber and wherein thecompression flow path includes the internal flow path. In certainembodiments, the compression-side accumulator comprises a first tubecomprising: a first tube housing comprising: a first outer surface and afirst inner surface, the first inner surface defining a first bore,wherein at least a first portion of the first outer surface is exposedto fluid in the first working chamber of the compression-sideaccumulator. In certain embodiments, the compression-side accumulatorcomprises a second tube comprising: a second tube housing including asecond outer surface and a second inner surface, the second innersurface defining a second bore, wherein at least a second portion of thesecond outer surface is exposed to fluid in the first working chamber ofthe compression-side accumulator. In certain embodiments, the secondbore has a second cross-sectional area that is larger than a firstcross-sectional area of the first bore (e.g., by a factor of at least 2or at least 5, and/or by a factor of less than 100).

In certain embodiments, the hydraulic apparatus further comprises anextension flow path fluidically coupling the pump to the extensionchamber, and an extension-side accumulator comprising: an extension-sideaccumulator housing defining a second internal volume that is divided,by a second barrier (e.g., a movable barrier (e.g., a slidable piston, abladder or portion thereof)), into a second contained chamber (e.g., achamber containing a compressible fluid (e.g., a gas)) and a secondworking chamber, wherein: the second working chamber is fluidicallycoupled to the pump via an extension-side first flow path; and thesecond working chamber is fluidically coupled to the compression chambervia an extension-side second flow path. In certain embodiments, theextension-side accumulator has a second stiffness and thecompression-side accumulator has a first stiffness, wherein the secondstiffness is greater than the first stiffness. For example, the secondstiffness may be equal to at least 5 times or at least 10 times thefirst stiffness. In certain embodiments, the second stiffness is greaterthan the first stiffness by a factor of less than 100. In certainembodiments, the first internal volume is larger than the secondinternal volume (e.g, by a factor of at least 2, by a factor of between2 and 100).

In certain embodiments, the extension-side accumulator may be a type-1accumulator. In certain embodiments, the extension-side accumulatorfurther comprises a cylindrical neck (e.g., having a diameter between4-10 mm and/or a length less than 5 mm) that fluidically couples thesecond working chamber to the extension flow path In certain embodimentsin which the extension-side accumulator is a type-1 accumulator, theextension-side first flow path may have a third length and theextension-side second flow path may have a fourth length, wherein thethird length is less than the fourth length.

In certain embodiments, the extension-side accumulator may be a type-2accumulator. In certain embodiments in which the extension-sideaccumulator is a type-2 accumulator, the extension-side first flow pathmay have a third length, the extension-side second flow path may have afourth length, and the third length may be greater than the fourthlength.

In certain embodiments, a third TFmag of a transfer function describinga relationship between pressure at a fourth point and pressure at afifth point has at least one of a global maximum and local maximum at athird frequency, wherein the fourth point is located in one of: of thepump and the extension-side first flow path, and the fifth point islocated in the second internal volume (e.g., inside the second workingchamber or inside the second contained chamber). Alternatively oradditionally, a third TFph of the third transfer function describing arelationship between pressure at a fourth point and pressure at a fifthpoint may be equal to +1-90° at a third frequency, wherein the fourthpoint is located in one of: the pump and the extension-side first flowpath, and the fifth point is located in the second internal volume(e.g., inside the second working chamber or inside the second containedchamber). In either case, in certain embodiments the third frequency ishigher than the first frequency. In certain embodiments, the thirdfrequency is larger than a third lower limit and lower than a thirdupper limit, wherein the third lower limit is 100 Hz and the third upperlimit is 500 Hz. In certain embodiments, the third frequency is lowerthan the aforementioned second frequency.

In certain embodiments, the compression-side accumulator housing may bedirectly physically attached to the actuator housing. In certainembodiments, the compression-side accumulator housing and the actuatorhousing may share at least a common portion (e.g., a common wall).

In certain embodiments, the hydraulic apparatus may further comprise anouter housing that encircles at least a portion of the actuator housing.In certain embodiments, the hydraulic apparatus may include an annularcavity bounded on one side by an outer surface of the actuator housingor a portion thereof, and on another side by an inner surface of theouter housing or a portion thereof. In certain embodiments, at least oneof the compression-side first flow path, the compression-side secondflow path, the extension-side first flow path, and the extension-sidesecond flow path includes at least a portion of the annular cavity. Incertain embodiments, an inner diameter of the outer housing is at least0.4 mm larger than an outer diameter of the actuator housing. In certainembodiments, a difference between the inner diameter of the outerhousing and the outer diameter of the actuator housing is less than 1mm. In certain embodiments, the annular cavity is separated a firstvolume and a second volume by an annular cavity (e.g., an o-ring).

In certain embodiments, a removable insert is inserted into a portion ofat least one of: the compression flow path, the extension flow path, thecompression-side first flow path, the compression-side second flow path,the extension-side first flow path, and the extension-side second flowpath. In certain embodiments, inserting the removable insert into the atleast one flow path thereby changes one or more properties (e.g., across-sectional area, an inertance, and impedance, a restriction, etc.)of the at least one flow path. In certain embodiments comprising anannular cavity at least partially defined by the outer housing and theactuator housing, the removable insert may be a sleeve at leastpartially inserted into the annular housing, such that insertion of thesleeve into the annular cavity changes a cross-sectional area of theannular cavity. In certain embodiments, the sleeve may be in physicalcontact with at least a portion of an outside surface of the actuatorhousing. Additionally or alternatively, the sleeve may be in physicalcontact with at least a portion of an inside surface of the outerhousing.

In certain embodiments, the first barrier of the compression-sideaccumulator is an accumulator piston having a first surface at leastpartially exposed to fluid in the contained chamber and a second surfaceat least partially exposed to fluid in the working chamber. In certainembodiments, a first line normal to the second surface of theaccumulator piston is parallel to a second line normal to at least oneof the first face and second face of the actuator piston. In certainembodiments, the compression-side accumulator housing comprises acylindrical portion having a first radial axis and a first longitudinalaxis and the actuator housing comprises a second cylindrical portionhaving a second radial axis and a second longitudinal axis, and thefirst longitudinal axis and the second longitudinal axis are parallel.

In certain embodiments, the compression-side accumulator includes afirst compliant arrangement configured to provide a first degree ofcompliance responsive to a first internal pressure within the firstinternal volume. The first compliant arrangement may comprise, forexample, a gas contained in the first contained chamber, and the firstbarrier may be moveable to compress or expand a volume of the firstcontained chamber. In certain embodiments, wherein the compression-sidefirst flow path comprises a first mass of fluid configured to resonatewith the first compliant arrangement at a first resonance frequency. Thefirst resonance frequency may vary responsive to variation of the firstinternal pressure. In certain embodiments, the compression-side secondflow path comprises a second mass of fluid configured to resonate withthe first compliant arrangement at a second resonance frequency. Incertain embodiments, the second resonance frequency is higher than thefirst resonance frequency.

In certain embodiments, extension-side accumulator comprises a secondcompliant arrangement in fluid communication with the second internalvolume, a neck, and a third mass of fluid located in the neck, whereinthe third mass is configured to resonate with the second compliantarrangement at a third resonance frequency (e.g., 5-100 Hz, 80-300 Hz).In certain embodiments, the second compliant arrangement comprises a gascontained in the second contained chamber, and the second barrier may bemoveable to compress or expand a volume of the second contained chamber.In certain embodiments, the third resonance frequency may be higher thanthe first resonance frequency.

In certain embodiments, the hydraulic apparatus contains fluid; the pumpcomprises a rotor, rotation of which at a constant speed for a giventime generates pressure pulsations in at least a portion of the fluid ofthe hydraulic apparatus; the first compliant arrangement is arranged toat least partially absorb a first portion of said pressure pulsations;and the second compliant arrangement is arranged to at least partiallyabsorb a second portion of said pressure pulsations. In certainembodiments, a first amplitude of the pressure pulsations at a firstpoint is larger than a second amplitude of the pressure pulsations at asecond point, wherein the first point is located in one of: the pump andthe compression-side first flow path and the second point is located inthe compression chamber of the actuator. In certain embodiments, a thirdamplitude of the pressure pulsations at a third point is larger than afourth amplitude of the pressure pulsations at a fourth point; whereinthe third point is located in one of: the pump and the extension-sidefirst flow path and the fourth point is located in the extension chamberof the actuator.

In certain embodiments, the hydraulic actuator of any of the disclosedhydraulic apparatuses described herein may further comprise a pistonhaving a first face exposed to fluid in the compression chamber and asecond face exposed to fluid in the extension chamber. Additionally, apiston rod may be attached to the second face.

In another aspect, a vehicle is disclosed comprising a suspension systemincluding a hydraulic apparatus according to any embodiment describedherein. In certain embodiments, the vehicle may comprise a plurality ofthe hydraulic apparatuses according to any of the embodiments disclosedherein.

In yet another aspect, an accumulator is disclosed comprising: a housingdefining a first internal volume that is divided, by a barrier (e.g., amovable barrier (e.g., a slidable piston, a bladder or portion thereof))into a first contained chamber (e.g., a chamber containing acompressible fluid (e.g., a gas)) and a first working chamber. Theaccumulator may further comprise a first tube having a first tubehousing comprising a first outer surface, and a first inner surfacedefining a first bore, wherein at least a first portion of the firstouter surface is exposed to fluid in the first working chamber of thecompression-side accumulator. The accumulator may further comprise asecond tube having a second tube housing comprising a second outersurface, and a second inner surface defining a second bore, wherein atleast a second portion of the second outer surface is exposed to fluidin the first working chamber of the compression-side accumulator. Incertain embodiments, the second bore has a second cross-sectional areathat is larger than a first cross-sectional area of the first bore. Forexample, the second cross-sectional area may be greater than the firstcross-sectional area by a factor of at least 2 or at least 5, or by afactor of between 2-100 or 5-100. Alternatively or additionally, thefirst tube may have a first length and the second tube may have a secondlength that is less than the first length. Alternatively oradditionally, a first ratio of the first length over the firstcross-sectional area may be greater than a second ratio of the secondlength over the second cross sectional area. Alternatively oradditionally, inertance of fluid in the first bore may be greater thaninertance of fluid in the second bore.

It should be appreciated that the foregoing concepts, and additionalconcepts discussed below, may be arranged in any suitable combination,as the present disclosure is not limited in this respect. It isenvisioned that any feature of any embodiment may be combined with anyother feature of any other embodiment. Further, other advantages andnovel features of the present disclosure will become apparent from thefollowing detailed description of various non-limiting embodiments whenconsidered in conjunction with the accompanying figures. Further, itshould be understood that the various features illustrated or describedin connection with the different exemplary embodiments described hereinmay be combined with features of other embodiments or aspects. Suchcombinations are intended to be included within the scope of the presentdisclosure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates TFmag of a pressure/pressure transfer functiondescribing a relationship between pressure at two points in a hydraulicsystem.

FIG. 2 illustrates a hydraulic system including a hydraulic actuator.

FIG. 3 illustrates a plot of observed pressure depicting pressure rippleat a first point in a hydraulic system.

FIG. 4 illustrates a hydraulic system including a hydraulic actuator anda type-1 accumulator.

FIG. 5 illustrates a hydraulic system including a hydraulic actuator anda type-2 accumulator.

FIG. 6 illustrates pressure/displacement transfer functions describingtransfer between various points in a hydraulic system including ahydraulic actuator and an accumulator.

FIG. 7 illustrates a hydraulic system including a hydraulic actuator andtwo type-1 accumulators.

FIG. 8 illustrates a hydraulic system including a hydraulic actuator, atype-1 accumulator, and a type-2 accumulator.

FIG. 9 illustrates a hydraulic system including a hydraulic actuator andtype-2 accumulators.

FIG. 10 illustrates a vehicle having a suspension system includinghydraulic actuators.

FIG. 11A illustrates another embodiment of a hydraulic system includinga hydraulic actuator and two accumulators.

FIG. 11B illustrates another embodiment of a hydraulic system includinga hydraulic actuator and two accumulators.

FIG. 12A illustrates an embodiment of a type-2 accumulator.

FIG. 12B illustrates another embodiment of a type-2 accumulator.

FIG. 12C illustrates another embodiment of a type-2 accumulator.

FIG. 13 illustrates TFmag of pressure/pressure transfer functionsdescribing relationships between pressure at various points in ahydraulic system.

FIG. 14 illustrates Tfph of various transfer functions describingrelationships of pressure at various points in a hydraulic system.

FIG. 15 illustrates propagation of a pressure wave through ahypothetical hydraulic system.

FIG. 16a illustrates a hydraulic system comprising a hydraulic actuator.

FIG. 16b illustrates a pressure/displacement transfer function of thehydraulic system of FIG. 16 a.

FIG. 17a illustrates a hydraulic system comprising a hydraulic actuator.

FIG. 17b illustrates a pressure/displacement transfer function of thehydraulic system of FIG. 17 a.

FIG. 18a illustrates a hydraulic system comprising a hydraulic actuator.

FIG. 18b illustrates a pressure/displacement transfer function of thehydraulic system of FIG. 18 a.

FIG. 19a illustrates a hydraulic system comprising a hydraulic actuator.

FIG. 19b illustrates a pressure/displacement transfer function of thehydraulic system of FIG. 19 a.

FIG. 20a illustrates a hydraulic system comprising a hydraulic actuator.

FIG. 20b illustrates a pressure/displacement transfer function of thehydraulic system of FIG. 20 a.

FIG. 21a illustrates a hydraulic system comprising a hydraulic actuator.

FIG. 21h illustrates a pressure/displacement transfer function of thehydraulic system of FIG. 21 a.

FIG. 22a illustrates a hydraulic system comprising a hydraulic actuator.

FIG. 22b illustrates a pressure/displacement transfer function of thehydraulic system of FIG. 22 a.

FIG. 23 illustrates a theoretical model of the hydraulic system shown inFIG. 19 a.

FIG. 24 illustrates empirical results obtained from altering theinertance of the compression-side first flow path of a hydraulic system.

FIG. 25a illustrates an embodiment of a hydraulic system comprising ahydraulic actuator (drawn to scale).

FIG. 25b illustrates an alternative view of the system of FIG. 25a(drawn to scale).

FIG. 25c illustrates an alternative view of the system of FIG. 25a(drawn to scale).

FIG. 25d illustrates an alternative view of the system of FIG. 25a(drawn to scale).

FIG. 26 illustrates empirical results obtained from evaluation of twodifferent hydraulic systems.

Drawings are not to scale unless specifically noted.

DETAILED DESCRIPTION

Disclosed herein are various methods and systems that utilize one ormore hydraulic actuators. Such hydraulic systems have been utilized in,for example, active suspension systems of automobiles that, ideally,call for compact packaging, fast response times, and low noiseoperation. The inventors have discovered that even slight changes inrelative arrangement of hydraulic components in integrated hydraulicsystems may profoundly affect the operating properties (e.g., noise,response time) and packaging requirements of the overall system. Herein,a number of discoveries are described related to hydraulic componentsand specific arrangements of said hydraulic components in a hydraulicsystem, such that a combination of compact packaging, fast responsetimes, and low-noise operation may be achieved. These discoveriesinclude, for example, incorporation of various types of accumulatorslocated at different parts in the hydraulic systems, as well as precisetuning of, for example, relative impedances, inertances, and/or lengthsof various flow paths of the hydraulic systems.

The inventors have recognized that the precise arrangement of hydrauliccomponents in a hydraulic system, such as, for example, a hydraulicsystem utilizing a hydraulic actuator, can have profound effects onnoise, response time, and packaging size associated with the hydraulicsystem, often in ways that are not readily predictable using a-prioriinformation. Often times, these considerations may represent trade-offs;for example, adding components such as noise absorbers may serve tomitigate acoustic noise, but may add bulk to the system and/or increaseresponse time, thereby precluding certain applications in which space ishighly limited and/or very fast response times are desired. Presentedherein are various hydraulic systems, and methods of use thereof, thatmay allow for one or more of low noise, fast response-time operation,while permitting flexibility and compactness in packaging. The variousembodiments described herein should not be limited to providing theseexemplary benefits and other possible benefits are also possible.

Particularly, in one aspect, in a hydraulic system including a hydraulicactuator and a pump, an accumulator may be incorporated for absorbingpulsations or vibrations, such as vibrations that may lead to noise, inthe system. The accumulator may include a working chamber that isfluidically coupled to the pump by a first flow path and fluidicallycoupled to a compression chamber of the actuator by a second flow path.Inventors have recognized that a variety of performance metrics (suchas, for example, noise attenuation capability and/or response-time) canbe improved by controlling the relative inertances of the first flowpath and the second flow path, and/or by controlling resonancefrequencies of various portions of the system. For example, noiseattenuation may be improved in a system in which inertance of the firstflow path is greater than inertance of the second flow path.Additionally or alternatively, noise attenuation may be improved bydesigning a hydraulic system such that a resonance associated withinteraction of inertance in the first flow path and compliance of theaccumulator occurs at a first frequency of less than 90 Hz (e.g., at afrequency range of 1-90 Hz, 1-50 Hz, or 1-20 Hz. Optionally, the secondflow path may be configured such that a resonance associated withinteraction of inertance in the second flow path and compliance of theaccumulator occurs at a second resonance frequency that is greater thanthe first frequency. As described in detail herein, resonancefrequencies of a system may be determined or evaluated empiricallythrough the use of transfer functions.

Inventors have further discovered that, for hydraulic apparatusescomprising a pump and an accumulator in which the pump is fluidicallycoupled to both the compression chamber (via a compression flow path)and an extension-chamber (via an extension flow path), two accumulatorsmay be utilized and configured such that they interact in a synergisticmanner. Specifically, a compression-side accumulator may be located onthe compression-flow path that fluidically couples the pump and acompression chamber of the actuator, while an extension-side accumulatormay be located on the extension-flow path that fluidically couples thepump to an extension chamber. As will be shown, locating eachaccumulator on either side of the pump (e.g., one on the extension sideand one on the compression side) as described may result in systemperformance (e.g., pulsation attenuation capability) that faroutperforms the sum of the individual accumulators considered alone.Further synergy may arise by configuring one of the accumulators (e.g.,the extension-side accumulator) to have a stiffness greater than that ofthe other accumulator (e.g., the compression-side accumulator) and/or bysizing one of the accumulators (e.g., the extension-side accumulator)such that it has an internal volume smaller than that of the otheraccumulator (e.g., the compression-side accumulator),

Alternatively or additionally, the compression-side accumulator mayinclude two distinct ports—a first port and a second port—through whichfluid may ingress/egress a working chamber of compression-sideaccumulator (for example, the compression-side accumulator may be atype-2 accumulator as described herein). In these embodiments, asdescribed in detail herein, the inventors have recognized thatadditional benefits may arise with respect to system performance byprecisely controlling various properties (e.g., a first inertance, afirst impedance, a first length, a first cross-sectional area) of acompression-side first flow path, or a portion thereof, fluidicallycoupling the pump to the first accumulator port relative to therespective properties (e.g., a second inertance, a second impedance, asecond length, a second cross-sectional area) of a compression-sidesecond flow path, or portion thereof, fluidically coupling the secondaccumulator port to the compression chamber of the actuator.

Turning now to the figures, several non-limiting embodiments are nowdescribed in detail. Turning now to the figures, several non-limitingembodiments are now described in detail. FIG. 2 illustrates a simplifiedembodiment of a hydraulic actuator 212. In the illustrated embodiment,the hydraulic actuator 212 includes (i) a compression chamber 201defined by a cylindrical housing 205 and a first face of a slidablepiston 207 inserted into the housing 205, and (ii) a extension chamber220 defined by a second face of the slidable piston 207 and the housing205. The second face of the slidable piston 207 may be physicallyattached to a piston rod 209. In the illustrated embodiment, the housing205 further comprises a receiving port 203, which may be, for example,an opening through the housing 205 that allows fluid to ingress oregress the compression chamber 201. The compression chamber 201 may befluidically coupled to a pump 206 by a receiving flow path 208, whichmay be, for example, a tube, hose, pipe, or channel. The pump, in turn,may be fluidically coupled to a fluid reservoir 210. An electric motor218, in communication with a motor controller 216, may be operativelycoupled to the pump 206.

In certain embodiments, a torque applied to the pump 206 by the electricmotor 218 may be intentionally varied with time in order to vary apressure of fluid in the compression chamber 201, thereby imparting aforce onto the piston 207 that may result in movement of the piston 207and attached piston rod 209, and may cause a length 214 of the hydraulicactuator to change. In various embodiments, a motor controller 216 mayreceive a nominal command profile (e.g., from an external controller ora user) that specifies, for example, any one of: a desired length 214 ofthe actuator 212 over a given time (i.e., a “nominal command lengthprofile”), a desired longitudinal position of the piston over a giventime (i.e., a “nominal command position profile”), a desired pumpvelocity over a given time (i.e, a “nominal command velocity profile”),a desired force to apply to the first face of the piston 207 over agiven time (i.e., a “nominal command force profile”), a desired pressureof the compression chamber 201 over a given time (i.e., a “nominalcommand pressure profile”), or a desired torque to apply to the pump 206over a given time (i.e., a “nominal command torque profile”). In certainembodiments, in response to receiving a nominal command profile, themotor controller 216 may apply a time-dependent signal (e.g., anelectrical signal (e.g., a current, a voltage)) to the motor 218 suchthat the pump and/or actuator behaves according to the nominal commandprofile.

A command position profile (describing desired longitudinal position ofthe piston over time) may be related to a command force profile(describing desired force to apply on the first face of the piston 207over time) by, for example, using the equationF(t)=m*d²x(t)/dt²+P_(b)A_(b), where x(t) is the position profile, m isthe mass of the piston and piston rod, Pb is the pressure of fluid inthe extension chamber 210, A_(b) is the area of the second face of thepiston exposed to fluid in the extension chamber 210, and F(t) is thecommand force profile. Likewise, a command velocity profile (describingdesired operating velocity of the pump over time) may be related to aposition profile by using, for example, the relationw(t)=dx(t)/dt*A*1/Disp, where x(t) is the position profile, A is thecross-sectional area of the compression chamber, Disp is thedisplacement per revolution of the pump 206, and w(t) is the commandvelocity profile in units of revolutions per unit time. It is noted thatthe above equation, which is intended as an example for purposes ofclarity, may be modified to include additional parameters such ascompressibility of the hydraulic fluid, leakage flow around the pump,etc. A command pressure profile (describing desired pressure of thecompression chamber 201 over time) may be determined based on a commandforce profile by, for example, using the equation P(t)=F(t)/A, where Ais the area of the first face of the piston 207 exposed to fluid in thecompression chamber 201 and P(t) is the command pressure profile. Acommand torque profile (describing desired torque to apply to the pump206 over time) may be determined based on a command pressure profileusing, for example, the equation τ(t)=[P(t)−Pr]*Disp, where Disp is thedisplacement volume of the pump, Pr is the pressure of fluid in thefluid reservoir 210, and τ(t) is the nominal command torque profile. Theaforementioned equations are examples and such equations may be modifiedto incorporate additional parameters, such as, for example, inertia ofthe pump, drag torque, friction of various components, leakage aroundthe pump, etc.

In certain embodiments, the pump 206 may be a positive displacementhydraulic pump. As a result of a phenomenon known as “pump ripple,” theflow rate of fluid discharged by a positive displacement pump may not besmooth, but rather may fluctuate at a frequency referred to as a “ripplefrequency.” Such fluctuations in discharge flow rate that originate at apump 206 (referred to herein as “flow ripple”) may generate pressurefluctuations that may propagate downstream in a hydraulic system aspressure waves (sometimes referred to as acoustic waves), therebyresulting in fluctuations in pressure differential at various points inthe hydraulic system.

FIG. 3 depicts an example of a pressure profile that may be observed ata first point 200 of the hydraulic system of shown in FIG. 2. As can beseen, the observed pressure 301 at the first point 200 in the hydraulicsystem fluctuates according to the command pressure profile 303 (whichspecifies desired pressure as a function of time) superimposed withhigher frequency fluctuations 305 that arise due to flow ripplegenerated by the pump 206. The high frequency fluctuations 305 inobserved pressure 301 that arise due to flow ripple may be referred toas “pressure ripple.” Returning to FIG. 2, if the pressure rippleobserved at the first point 200 is able to propagate through thereceiving flow path 208 and into the compression chamber 201, then theforce exerted on the piston 207 may fluctuate, potentially resulting influctuations in a position of the piston 207 and piston rod 209. Thisripple may be transferred to the piston rod 209 and to any structure towhich the piston rod 209 is attached, such as, for example, a top mountand/or a vehicle body. As used herein, the term ripple may refer to flowripple, pressure ripple, or force ripple, as all aforementionedphenomena are interrelated and may share a common origin (e.g.,operation of a positive displacement pump).

If allowed to propagate through a hydraulic system, ripple may generateaudible noise or other instability in a hydraulic system and/or thestructures to which it is attached. Therefore, in various applications,it may be desirable to design a hydraulic system in which pressureripple is unable to propagate through a hydraulic system or is at leastpartially mitigated during propagation. Mitigation of acousticpropagation may be accomplished by, for example, using a component knownas an accumulator downstream of the pump. FIG. 4 illustrates the use ofa hydraulic accumulator 402. The hydraulic system of FIG. 4 is similarto that of FIG. 2, with the addition of an accumulator 402 that has beenlocated on the receiving flow path. An accumulator 402 may include ahousing 416 that defines an internal volume 401. As shown, the internalvolume 401 may be separated, by a barrier 406, into a contained chamber408 and a working chamber 410. In certain embodiments, a first side ofthe barrier 406 is exposed to a compressible fluid (e.g., a gas)contained in the contained chamber 408, and a second side of the barrier406 is exposed to hydraulic liquid in the working chamber 410.

The compressible fluid in the contained chamber 408 may be separatedfrom the working chamber by the barrier. The barrier 406 may be movable.In certain embodiments, a pressure pulsation may result in instantaneouspressure of fluid in the receiving chamber exceeding the pressure of thecontained chamber. In response, fluid may flow from the receiving flowpath 208, through the port 450, and into the working chamber 410,potentially resulting in movement (e.g., sliding or flexing) of thebarrier 406 such that the volume of the working chamber 410 increaseswhile the volume of the contained chamber 408 contracts; due tocontraction of the volume of the contained chamber, the compressiblefluid in the contained chamber 408 may subsequently exert a restoringforce on the barrier 406. As the pressure of fluid in the receivingchamber returns to a nominal value, the restoring force may cause thebarrier 406 to move back to its original position simultaneously asfluid flows out of the working chamber 410 through the port 450. In thisway, the compliance provided by the compressible fluid in the containedchamber may allow for pulsations to be at least partially absorbed bythe accumulator.

In the illustrated embodiment, the barrier 406 is a floating piston andthe housing 416 is cylindrical. However, in various embodiments, thehousing 416 may be any shape including spherical and semispherical, andthe barrier 406 may be any barrier, such as, for example, an elastomericor semi-elastomeric bladder, that separates fluid in the containedchamber 408 from fluid in the working chamber 410. In the embodiment ofthe accumulator 402 illustrated in FIG. 4, the accumulator housing 416comprises a single port 450 through which fluid may egress/ingress theworking chamber 410 to/from the receiving flow path 208. An accumulatorin which fluid may egress and ingress the working chamber 410 through asingle port 450 (as opposed to multiple ports) is referred to herein asa type-1 accumulator. The hydraulic accumulator 402 of FIG. 4 maytherefore be said to be a type-1 accumulator.

It should be understood that hydraulic accumulators can be provided invarious configurations including but not limited to hydraulic gascharged accumulators (wherein the contained chamber 408 includes a gas)and spring hydraulic accumulators (wherein the barrier 406 is physicallyrestrained via a spring). While many of the embodiments described hereindepict hydraulic gas accumulators, the current disclosure is not limitedin this fashion of accumulators except as explicitly stated. It isunderstood that, unless otherwise stated, the various systems describedherein may correspond to any appropriate type of accumulator. It isunderstood that other terms know in the art, depending on context, maybe used interchangeably with accumulator, such as, for example, a bufferand a reservoir.

The tendency of a disturbance at one point of a hydraulic system topropagate and effect components at other points in the hydraulic systemmay be characterized qualitatively and/or quantitatively using transferfunctions. A transfer function, as used herein, is understood to mean afunction that describes how changes in an observed operating parameterat a second point in a system are related to changes in an operatingparameter at a first point in the system. The observed operatingparameter at the second point may be referred to as, for example, an“output” and may correspond to, for example, an observed pressure, aforce applied to the piston, a displacement position, etc. The change atthe first point may be referred to as, for example, an “input” (such as“input ripple”) and may correspond to, for example, a pressure ripple atfirst point, a displacement, etc. Response of hydraulic systems to inputripple generally may depend on the frequency of the input ripple. Incertain embodiments, therefore, a transfer function may be representedas a plot depicting, on the y-axis, a ratio (or log ratio) of intensityor amplitude of the output to intensity or amplitude of the input and,on the x-axis, frequency of the input (e.g. input ripple).

FIG. 1 depicts an example of a transfer function 100. In the illustratedexample, the y-axis 102 corresponds to a ratio of intensity (oramplitude of, for example, pressure fluctuations observed at a secondpoint 404 of the hydraulic system of FIG. 4 to intensity or amplitudeof, for example, the pressure fluctuations observed at a first point 200of the hydraulic system of FIG. 4. In the particular example shown, thefirst point 200 is located in the receiving flow path 208 between thepump 206 and the accumulator 402, and the second point 404 is located inthe working chamber 404 of the accumulator 402. However, these pointsare merely exemplary, and in general a transfer function may describetransfer of, or a relationship between, pulsations between any twopoints in a system.

In the illustrated embodiment, the x-axis 104 may correspond tofrequency of the pressure fluctuation at the first point 200. If apressure fluctuation at a given frequency propagates from the firstpoint 200 to the second point 404 with no attenuation nor amplification,then the transfer function 100 would be 1 at that given frequency (thatis, the intensity or amplitude of the pressure when it reaches thesecond point 404 would be equal to the initial intensity or amplitude ofthe pressure at the first point 200). For a fluctuating pressure that isattenuated during propagation from the first point 200 to the secondpoint 404, or for a pressure wave where the energy is partially directedto an alternate flow path that does not pass through the second point404, the transfer function 100 may be less than 1. For pressurefluctuations that are amplified during propagation, the transferfunction 100 may be greater than 1.

Transfer functions may also be illustrated in a graph where the y-axis102 may be represented as a log of the ratio of output intensity toinput intensity. In these plots (which use a log-scale, or dB scale, forthe y-axis), a zero value indicates no attenuation and no amplificationduring propagation of an input pressure from a first point to a secondpoint; a negative value indicates attenuation during propagation; and apositive value indicates amplification during propagation.

As discussed above, the exemplary transfer function illustrated in FIG.1 illustrates a hypothetical response of pressure at the second point404 (the output) of the hydraulic system in response to pressurefluctuations at a first point 200 (the input) of the hydraulicsystem—the ratio along the y-axis therefore represents pressureintensity or amplitude over pressure intensity or amplitude. These typesof transfer functions, in which a relationship of pressure at one pointto pressure at another point is described, may be referred to as“pressure/pressure transfer functions.”

In alternate illustrations, the y-axis may represent ratios of intensityor amplitude of any parameter at the output over intensity or amplitudeof another parameter at the input. For example, in certainillustrations, the y-axis may correspond to a ratio of (a) intensity ofan observed pressure wave at the second point 404 of the hydraulicsystem over (b) intensity of fluctuating fluid displacements (referredto as displacement ripple) determined at a first point 200 of thehydraulic circuit. In these embodiments, the ratio is of pressureintensity or amplitude at the output over displacement at the input, andthe transfer function is referred to as a pressure/displacement transferfunction. Alternatively, for example, in certain representations of atransfer function may be obtained by plotting, on the y-axis, a ratio of(a) the position of the barrier 406 (or other moveable component) of theaccumulator 402 to (b) fluctuations in pressure at the first point 200of the hydraulic system; in these embodiments, the ratio is ofdisplacement at the output over pressure intensity or amplitude at theinput.

The exemplary magnitude of the pressure/pressure transfer functionillustrated in FIG. 1 corresponds to transfer (or propagation) ofpressure pulsations (sometimes referred to as pressure waves or aspressure pulsations) between the first point 200 of FIG. 4 to the secondpoint 404 of FIG. 4. As can be seen in FIG. 4, the first point 200 islocated in the flow passage in between the pump 206 and the accumulator402, while the second point 404 is located within the working chamber410 of the accumulator 402. In the exemplary transfer function 100illustrated in FIG. 1, the transfer function 100 is flat and equal to 1for a lower range of frequencies 106, indicating that a pressure wave ata frequency within the lower range of frequencies 106 is transferredwithout mitigation to the second point 404. The transfer function thenreaches a maximum 108 at a specific frequency 109 that may be referredto as a “resonance frequency” (which may be, for example, a Helmholtzresonance frequency). In other transfer functions, such as, for example,pressure/displacement transfer functions, a resonance frequency may beindicated by a minimum instead of a maximum.

The transfer functions disclosed thus far all describe a ratio ofintensity or amplitude of a parameter (e.g., pressure) at one point tointensity or amplitude of a parameter (e.g., pressure, displacement) ata second point. Additionally or alternatively, a transfer function maybe generated that describes the phase of a wave (e.g., pressure wave, orfluctuation) at a given frequency observed at one point in the hydraulicsystem as compared to the phase observed for the same frequency atanother point in the hydraulic system. For example, FIG. 15 depicts ahypothetical hydraulic system comprising a hydraulic element 1501. Asshown in FIG. 15, a pressure wave or fluctuation 1507 generated at afirst point 1503 in the hydraulic system propagates through thehydraulic element 1501 to a second point 1505 (that is, the pressurewave or fluctuation is transferred from the first point to the secondpoint). As depicted for the hypothetical hydraulic system of FIG. 15,the intensity or amplitude 1509 of the pressure wave 1507 at the firstpoint 1503 is equal to the intensity or amplitude 1511 of the pressurewave 1507 at the second point 1505, so a magnitude of apressure/pressure transfer function plotting the log ratio of theamplitude 1511 of the pressure wave 1507 at the second point 1505 to theamplitude 1509 of the pressure wave 1507 at the first point 1503 wouldbe equal to zero (indicating propagation without attenuation oramplification) for the specific frequency of wave shown. However, as canbe seen, as the pressure wave propagates through the imaginary element1501, its phase is shifted by 180 degrees. Therefore, the phase of thetransfer function describing propagation from the first point 1503 tothe second point 1505 would be equal to +/−180° for the specificfrequency of wave shown.

For the sake of clarity and brevity, rather than referring to the“magnitude of a transfer function” and the “phase of the transferfunction”, the following terminology is employed. As used herein theterm “TFmag” of a transfer function is understood to mean the magnitudeof a complex function, and the term “TFph” is understood to mean thephase of a complex function. Therefore, the TFmag of a transfer functiondescribing a relationship between pressure at a first point and pressureat a second point may be represented as a plot having two axes (e.g., anx-axis and a y-axis) in which the first axis (e.g., x-axis) depictsfrequency of pressure fluctuations and the second axis (e.g., y-axisdepicts) a ratio (or log-ratio) of amplitude of pressure fluctuations atthe second point to amplitude of pressure fluctuations at the firstpoint. Similarly, the TFph of a transfer function describing arelationship between pressure at a first point and pressure at a secondpoint may be represented as a plot having two axes (e.g., an x-axis anda y-axis) in which the first axis (e.g., x-axis) depicts frequency ofpressure fluctuations and the second axis (e.g., y-axis) depicts thephase angle of the transfer function (e.g., a difference between thephase of pressure fluctuations at the second point as compared to thephase of pressure fluctuations at the first point). “Phase difference”is understood to refer to a difference in the phase of pressurefluctuations as observed at one point in a hydraulic system compared tothe phase of the pressure waves as observed at another point in thehydraulic system.

When a portion of a hydraulic system between two points is in resonance,there may be a 90° phase difference between the variations of thepressures at the two points. Alternatively stated, the TFph of atransfer function describing a relationship between pressures at the twopoints may have a value of ⁺/⁻90° at the resonance frequency of thatportion of the system. Additionally, as discussed above, the TFmag ofthe transfer function may have a local maximum or global maximum at theresonance frequency of that portion of the system. However, in certainsystems, for example heavily damped systems, it may be difficult toidentify a local maximum from a plot of TFmag (e.g., the maximum may notrise above noise levels); in these cases, for example, the resonancefrequency may be determined by evaluating the TFph to determine afrequency (or frequency range) at which the observed phase difference is⁺/⁻90°.

The term “resonance frequency,” as used herein, therefore may refer to,for example, (i) a frequency at which a TFmag of a pressure/pressuretransfer function shows either a global maximum or local maximum (i.e.,a frequency at which the first derivative of the transfer function withrespect to frequency changes from a positive value to zero or from apositive value to a negative value), or (ii) a frequency at which a TFphis equal to ⁺/⁻90°.

When pulsations having a frequency corresponding to a resonancefrequency are introduced into a fluid-filled hydraulic system, thepulsations may “excite” one or more resonances in the system. Withoutwishing to be bound to any particular theory, such resonance may bethought of as occurring when an inertial element of the hydraulic system(for example, a portion of the fluid in a volume of the hydraulicsystem) physically oscillates synchronously with a compliant element(e.g., a gas contained in the contained chamber of an accumulator, aspring) of the system, such that there exists a continuous exchangebetween potential energy (e.g., energy stored by compression orextension of the compliant element) and kinetic energy (e.g., due tomovement of the portion of fluid). In general, a hydraulic systemfeaturing a plurality of inertial and compliant elements may exhibitvarious resonances. If two or more of these various resonances haveoverlapping or sufficiently similar frequencies, then a first resonanceof the hydraulic system may ‘excite’ a second resonance of the hydraulicsystem in an uncontrollable or undesirable manner. Therefore, inventorshave recognized the importance of designing the system such that variousresonances are sufficiently spaced apart in resonance frequency, as willbe discussed throughout this application.

In view of the above, a resonance frequency of a given hydraulic systemmay be determined, for example, by: (i) locating pressure sensors atvarious points in the hydraulic system, (ii) introducing pressure wavesor pulsations having a first frequency into the system, (iii) monitoringthe intensity, amplitude, and/or phase of the pressure wave orpulsations at each of the various points in the system, (iv) varying thefrequency of the generated pressure waves or pulsations while continuingto monitor the intensity, amplitude, and/or phase of the pressure waveor pulsations at each of the various points in the system, (v)determining TFmag and/or TFph of one or more transfer functionsdescribing the relationship between pressures at the various points, and(vi) identifying frequencies where the TFph is +/−90° and/or the TFmaghas a global or local maximum.

Returning to FIG. 1, at a second range of frequencies 110 higher thanthe resonance frequency 109, the transfer function decreases below 1,indicating that a pressure fluctuation with a frequency in the secondrange will either be attenuated during propagation or will follow analternate flow path that does not pass through the second point 404.Without wishing to be bound to any particular theory, at frequencies inthe low frequency range 106, the hydraulic actuator 212 may have a highfluidic impedance as compared to the accumulator 402. As fluid tends toflow primarily via the pathway with the lowest impedance, at lowfrequencies, pressure pulsations may propagate to the working chamber410 of the accumulator 402, causing the barrier 406 to move up and downin response to the pressure pulsations, thereby at least partiallyabsorbing their energy and, for example, converting it to heat energy(via, for example, heating of the gas particles in the contained chamber408). As a result, low frequency input pressure pulsations may propagateinto the working chamber 410 of the accumulator 402, and, in certaincases, may be absorbed by the accumulator 402.

Pressure fluctuations with a frequency at or substantially near theresonance frequency 109 may be amplified between the first point 200 ofFIG. 4 to the second point 404 of FIG. 4—a phenomenon that may bereferred to as “Helmholtz” type resonance—resulting in a local maximum108 in the TFmag at the resonance frequency 109. On the other hand,pressure fluctuations with a frequency in a second range 110 higher thanthe resonance frequency 109 may not be able to overcome inertiaassociated with movement of the barrier 406 and/or inertia associatedwith movement of fluid in the neck 452 of the accumulator. At thesehigher frequencies, the fluid in the neck 452 may remain effectivelyimmobile, such that fluid flows through the receiving path 208 withoutingressing/egressing the working chamber 410 of the accumulator. Theaccumulator, therefore, may become less effective or not effective atabsorbing pressure fluctuations (e.g. ripple) as the frequencyincreases. For these reasons, for a system such as that shown in FIG. 4that employs a type-1 gas accumulator, a typical Tfmag of a transferfunction may follow the general pattern of FIG. 1 (e.g., a relativelyflat portion initial corresponding to low frequency range 106, a maximum108 corresponding to a resonance frequency 109, and a negative slope ina second range of frequencies 110).

Based on the foregoing, the inventors have recognized that a type-1accumulator (e.g., an accumulator 402 that branches off the flow path208 via a neck 452) may become progressively less effective at absorbingfluctuations (e.g. ripple) as frequency increases above a resonancefrequency 109 of the portion of the system. For ripple with frequenciessufficiently greater than the resonance frequency 109, the effectivenessof the accumulator 402 may diminish to such a degree that response ofthe overall hydraulic system may approach that of a similar hydraulicsystem with no accumulator.

The inventors have recognized that, in certain hydraulic systemscomprising hydraulic actuators, an alternative accumulator design,referred to herein as a “type-2 accumulator,” may result in moreeffective attenuation properties over a wider range of frequencies thatafforded by a type-1 accumulator. FIG. 5 illustrates use of a type-2accumulator Like a type-1 accumulator, a type-2 accumulator may includean accumulator housing 416 at least partially defining an internalvolume that is separated by a movable barrier 406 into a containedchamber 408 and a working chamber 410. As opposed to the type-1accumulator 402 shown in FIG. 4, the type-2 accumulator 500 shown inFIG. 5 may be characterized by the fact that the accumulator housing 416may include two distinct ports: (i) a first port 501 through which fluidmay ingress/egress the working chamber 410, and (ii) a second port 502through which fluid may also ingress/egress the working chamber 410.Furthermore, the first port and second port may be fluidically coupledby an internal flow path that may be located within the working chamber410. In the illustrated embodiment, the first port 501 allows fluid toingress/egress the working chamber 410 from/to a first flow path 505that fluidically couples the pump 206 to the working chamber 410, andthe second port allows fluid to ingress/egress the working chamber 410from/to a second flow path 507 that fluidically couples the workingchamber 410 to the compression chamber 201 of the hydraulic actuator 212

In a system with a type-2 accumulator 500, at least two distinct,non-overlapping flow paths may exist through which fluid mayingress/egress the working chamber 410 of the accumulator 500. Anoverall flow path between the pump 206 and the compression chamber 201of the hydraulic actuator 212 therefore includes the first flow path505, the working chamber 410 of the accumulator, and the second flowpath 507.

FIG. 6 illustrates the plot of TFmag 602 of a firstpressure/displacement transfer function describing the relationship ofpressure observed at a first point 552, located in the first flow path505, to a displacement ripple generated at the pump 206. FIG. 6 furtherillustrates TFmag 604 of a second pressure/displacement transferfunction describing to the relationship of pressure observed at a secondpoint 550, located inside of the working chamber 410 of the accumulator500, to the displacement ripple generated at the pump 206. Withoutwishing to be bound to any particular theory, as shown by thecorresponding Tfmags depicted in FIG. 6, propagation of fluctuations(e.g. ripple) between the pump 206 to the second point 550 locatedinside the working chamber 410 may be attenuated at a much wider rangeof input ripple frequencies as compared to propagation of the samedisplacement ripple to the first point 552 located in the first flowpath 505. Accordingly, as shown in FIG. 6, Tfmag 604 of the secondtransfer function may depict a local minimum at a second resonancefrequency 606 that is higher (i.e., is at a higher frequency) than afirst resonance frequency 608 depicted, as a local minimum, in TFmag 602of the first transfer function. The difference between the firstresonance frequency 608 and the second resonance frequency 606 mayresult from the inertial mass associated with fluid within the firstflow path 505. As frequency increases, a greater force may be requiredto cause oscillatory motion of the mass of this fluid quantity. As aresult of the type-2 design, points downstream of the accumulator 500(e.g., points located in the receiving flow path 507 or compressionchamber 201) may respond as if it they are being excited not by thedisplacement ripple or pressure fluctuations generated at the pump 206,but rather by the attenuated pressure ripple that has reached theworking chamber 410.

Returning to FIG. 5, the exemplary type-2 accumulator 500 includes twoports (the first port 501 and second port 502), each of which is influid communication with a first flow path 505 and a second flow path507, respectively. Without wishing to be bound to any particular theory,fluid in the first flow path 505 may interact with the compliance of theaccumulator to exhibit a first resonance (e.g., a first “Helmholtz” typeresonance, wherein a portion of fluid in the first flow path 552oscillates synchronously with the compliant arrangement of theaccumulator 500) at a first resonance frequency that depends at least inpart on a first mass of fluid (or first inertance) in the first flowpath 505 and/or the stiffness of the accumulator 500, while fluid in thesecond flow path 507 can interact with the compliance of the accumulator500 to exhibit a second resonance (e.g., a second “Helmholtz” typeresonance, wherein a portion of fluid in the second flow path 507oscillates synchronously with the compliant arrangement of theaccumulator) at a second resonance frequency that depends at least inpart on a second mass of fluid (or fluid inertance) in the second flowpath 507. By contrast, a type-1 accumulator 402, such as that shown inFIG. 4, includes only a single port 450 through which fluid mayingress/egress the working chamber 410 of the accumulator and maytherefore exhibit only a single fundamental resonance; this resonancemay be determined by the fluid in the neck 452 (i.e., a volume having asmaller cross-sectional area than the internal volume of the accumulatorthat directly fluidically couples the accumulator to the receiving flowpath 208) or a portion thereof oscillating synchronously with thecomplaint arrangement of the accumulator 402, and this resonancefrequency may depend on, for example: the cross sectional area of theneck 452, the length of the neck 452, the compliance or stiffness of theaccumulator 500, and/or the physical properties (e.g., compressibility,density) of the fluid in the neck 452.

In certain applications, it may be useful to fluidically couple abidirectional pump to both a compression chamber and an extensionchamber of a hydraulic actuator, thereby allowing the bidirectional pumpto directly control flow into (and fluid pressure of) either chamber. Anembodiment of such a system is shown in FIG. 7. In the illustratedembodiment, an actuator 700 comprises an actuator housing 702 into whicha piston 708 is slidably received. A first face 710 of the piston 708 isexposed to fluid in a compression chamber 706, while a second face 712of the piston 708 is exposed to fluid in an extension chamber 704. Apiston rod 714 may be physically attached to the second face 712 of thepiston 708. In alternate embodiments, the piston rod 714 may bephysically attached to the first face 710 of the piston 708. The pistonrod 714 may allow, in certain conditions, for the actuator to apply aforce to an external structure (e.g., a vehicle body (not shown)) thatmay be attached to the piston rod 714. In some embodiments, the pistonrod may be attached to the vehicle body through an intervening top-mount(not shown).

The illustrated hydraulic system also includes a compression flow path724 (indicated by dashed horizontal lines) fluidically coupling thecompression chamber 706 to the pump 718. The compression flow path 724may, in certain conditions, permit fluid to flow between the pump 718and the compression chamber 706 of the actuator. As a result, in certainconditions the pump may be utilized to drive fluid to the compressionchamber 706, thereby effecting a force on the first face 710 of thepiston and allowing for controlled extension of the piston rod 714. Asillustrated, the compression flow path may include, for example: (i) acompression-side accumulator 726, (ii) a compression-side first flowpath 728 fluidically coupling the pump 718 to a compression-side workingchamber 738 a of the compression-side accumulator 726, and (iii) acompression-side second flow path 730 fluidically coupling thecompression-side working chamber 738 a of the compression-sideaccumulator 726 to the compression chamber 706 of the actuator 700. Inthe illustrated embodiment, the compression-side accumulator 726 islocated fluidically between the pump 718 and the compression chamber706, and, in addition to serving other functions, may at least partiallyattenuate pulsations generated at the pump prior to said pulsationsreaching the compression chamber 706.

The illustrated hydraulic system further comprises an extension flowpath 716 (indicated by gray diagonal hatch marks) fluidically couplingthe extension chamber 704 of the actuator 700 to the pump 718. Theextension flow path 716 may, in certain conditions, permit fluid to flowbetween the pump 718 and the extension chamber 704 of the actuator. As aresult, in certain conditions the pump may be utilized to drive fluid tothe extension chamber 704, thereby effecting a force on the second face712 of the piston and allowing for controlled contraction of the pistonrod 714. The extension flow path may include: (i) an extension-sideaccumulator 720, (ii) a extension-side first flow path 722 fluidicallycoupling the pump 718 to the extension-side working chamber 738 b of theextension-side accumulator 720, and (iii) an extension-side second flowpath 701 coupling the extension-side working chamber 738 b of theextension-side accumulator 620 to the extension chamber 704 of theactuator 700. In the illustrated embodiment, the extension-sideaccumulator 720 is located fluidically between the pump 718 and theextension chamber 704, and, in addition to serving other functions, mayat least partially attenuate pulsations generated at the pump prior tosaid pulsations reaching the extension chamber 704.

In a preferred embodiment, the bidirectional pump is a variable speedpump, such that pressure difference and/or flow rate between thecompression chamber and extension chamber of the actuator may beprecisely controlled using the pump. In certain embodiments, the pump718 may comprise a rotor that includes, or is mechanically coupled to,one or more displacement elements (not pictured). In these embodiments,application of appropriate torque to the rotor may cause rotation of therotor, thereby generating a pressure difference and/or fluid flow acrossthe pump 718. Further, due to the aforementioned phenomenon of pumpripple, rotation of the rotor may also generate pressure pulsations(ripple) as described in FIG. 3 and the accompanying description herein.The pressure difference across the pump, flow rate across the pump,and/or frequency of the pressure pulsations may depend at least in parton an angular speed at which the rotor is rotated and/or a magnitude oftorque applied to the rotor.

The compression flow path 724, compression-side first flow path 728,compression-side second flow path 730, extension flow path 716,extension-side first flow path 722, and/or extension-side second flowpath 701 may comprise additional hydraulic components such as, forexample, one or more valves (e.g., variable flow valves, solenoidvalves, on/off valves, three way valves, etc.), restriction orifices, orother hydraulic components through which, under appropriatecircumstances (e.g., appropriate fluid pressure and/or opening of saidvalves), fluid may flow. Additionally or alternatively, in certainembodiments a length of the compression flow path 724 may exceed alength of the extension flow path 716. In certain embodiments, thelength of the compression flow path 724 may be larger than the length ofthe extension flow path by a factor of at least 2.

In the illustrated embodiment, each of the compression-side accumulator726 and the extension-side accumulator 720 comprises a housing 733 a and733 b, respectively, defining an internal volume 732 a and 732 b,respectively, with the internal volume being separated, by a barrier 736a and 736 b, respectively (e.g., a piston or bladder), into a containedchamber 734 a and 734 b, respectively and a compression-side and anextension side working chamber 738 a and 738 b, respectively. In theillustrated embodiment, each of the compression-side accumulator 726 andextension-side accumulator 720 further comprises a single port 735 a and735 b, respectively, defined as an opening through the housing 733 a and733 b, respectively, through which fluid may ingress/egress thecompression-side working chamber 738 a and 738 b, respectively. Each ofthe illustrated compression-side accumulator 726 and extension-sideaccumulator 720 may therefore be classified as type-1 accumulators. Aswill be discussed further, in various embodiments the compression-sideaccumulator 726 may be a type-1 accumulator or a type-2 accumulator.Likewise, in various embodiments, the extension-side accumulator 720 maybe a type-1 accumulator or a type-2 accumulator.

Without wishing to be bound to any particular theory, in the illustratedhydraulic system of FIG. 7, a net force applied to the piston 708 isequal to the difference of a first force applied to the first face 710of the piston 708 due to pressure of fluid in the compression chamber706 and a second force applied to the second face 712 of the piston 708due to pressure of fluid in the extension chamber 704. Depending on thetransfer function of the hydraulic system, displacement ripple generatedat the pump 718 (e.g., due to pump ripple) may propagate through thecompression flow path 724 to result in pressure fluctuations (pressureripple) in the compression chamber 706, and/or may propagate through theextension flow path 716 to result in pressure fluctuations (pressureripple) in the extension chamber 704. As will be described later,following extensive testing and analysis, the inventors have recognizedthat, as long as displacement ripple can propagate through at least oneof the compression flow path 724 and the extension flow path 716 andreach the compression and or extension volumes, the net force applied onthe piston 708 may fluctuate accordingly. That is, even if the ripple iscompletely attenuated through one of the aforementioned flow paths, ifthe ripple is able to propagate through the other flow path then the netforce on the piston may fluctuate (e.g., force ripple will occur),possibly causing the position of the piston to fluctuate or vibrateuncontrollably and undesirably. Therefore, in certain applications itmay be desirable to have two accumulators disposed along the flow paths(i.e., the extension-side accumulator 720 and the compression-sideaccumulator 726), each accumulator located and configured on oppositesides of the pump, such that propagation of input ripple through boththe compression flow path 724 and the extension flow path 716 from thepump may be at least partially or sufficiently mitigated, and in someinstances substantially eliminated, for at least some ripple frequenciesor frequencies within within a given frequency range.

The inventors have further recognized that size or relative size of thecompression-side accumulator 726 and/or extension-side accumulator 720may affect behavior of the system. On one hand, decreasing the size ofone or both of the internal volumes 732 a and 732 b of thecompression-side accumulator 726 and/or extension-side accumulator 720,respectively, and/or increasing the stiffness of one or both of theaccumulators may increase a resonance frequency associated with therespective accumulator(s), thereby increasing the range of frequenciesat which ripple is attenuated during propagation through the compressionflow path 725 and/or extension flow path 716. On the other hand, it maybe desirable to design the size and/or stiffness of one or both of theaccumulators such that expansion of fluid in the system due to changingtemperature, as well as displacement of fluid caused by insertion of thepiston rod into the actuator housing during compression, may be readilyaccommodated by one or both of the accumulators. Further, whileincreasing stiffness of an accumulator may increase the range offrequencies at which pulsations are attenuated, such increased stiffnessmay correspondingly decrease the magnitude of pulsation attenuation thatis achieved by the accumulator.

Inventors have determined that, in certain applications, theaforementioned trade-offs may be resolved by designing the system suchthat (a) one of the compression-side accumulator and extension-sideaccumulator has an internal volume that is substantially larger than theinternal volume of the other accumulator, and/or (b) one of theaccumulators is substantially stiffer than the other accumulator. Thistrade-off permits effective mitigation of ripple while maintainingoverall response of the system.

In a preferred embodiment, the internal volume 732 a of thecompression-side accumulator 726 is larger than the internal volume 732b of the extension-side accumulator 720 and/or the extension-sideaccumulator 720 is stiffer than the compression-side accumulator 726.Without wishing to be bound to any particular theory, if a hydraulicsystem such as that of FIG. 7 is to be in a vehicular suspension system,compression of the actuator 700 (e.g., due to driving over a bump in aroad) may result in fluid flowing from the compression chamber 706either to the compression-side accumulator 726 or through the pump 718.Likewise, extension of the actuator 700 (e.g., due to driving over apothole in a road) may result in fluid flowing from the extensionchamber 704 to either the extension-side accumulator 720 or through thepump 718. Inventors have recognized that, during operation of a vehicle,compression of dampers of a suspension system may occur at a maximumvelocity that is faster than extension of the dampers. Very rapidcompression of the actuator 700 may result in high fluid velocitiesthrough the pump 718, and may cause the pump 718 to rotate at velocitiesabove design specifications, possibly damaging the pump 718 or resultingin degradation in ride quality. Increasing the size of the internalvolume 732 a of the compression-side accumulator 726 (relative to thesize of the internal volume 732 b of the extension-side accumulator 720)may increase the fluid holding capacity of the compression-sideaccumulator 726, such that, during compression events, more fluid flowsto the compression-side accumulator 726 and less fluid flows through thepump 718, thereby potentially protecting components of the pump fromoverly rapid rotation and potentially allowing for improved ride qualityduring high speed compression events.

In certain embodiments, therefore, the internal volume 732 a of thecompression-side accumulator 726 may be larger than the internal volume732 b of the extension-side accumulator 720 by a factor of at least 2.In certain embodiments, the compression-side accumulator 726 has aninternal volume 732 a between 8 cubic inches and 13 cubic inches, andthe extension-side accumulator 720 has an internal volume 732 b between2.5 and 5 cubic inches, although embodiments outside these ranges arealso contemplated to be within the scope of the present disclosure. Incertain embodiments, the internal volume of an accumulator is understoodto mean a sum of the volume of the contained chamber 734 a or 734 b, thevolume of the barrier 736 a or 736 b, respectively, and the volume ofthe compression-side working chamber 738 a or 738 b, respectively. Inalternate applications (such as, for example, applications in whichextension of the actuator 700 is expected to occur at maximum velocitiesfaster than compression of the actuator 700), the hydraulic system maybe designed such that the internal volume 732 b of the extension-sideaccumulator 720 is larger than the internal volume 732 a of thecompression-side accumulator 726.

Likewise, in certain embodiments, the stiffness of the extension-sideaccumulator 720 may be at least 5 times the stiffness of thecompression-side accumulator 726. “Stiffness” of an accumulator isunderstood to refer to a ratio of the magnitude of a force exerted onthe barrier 406 of an accumulator or a portion thereof to the change ina physical dimension of the contained chamber 408. The stiffness of anaccumulator (and therefore the compliance and/or associated resonancefrequency) having a compliant arrangement that includes a compressiblefluid (e.g., gas) contained in a contained chamber, as disclosed herein,may vary responsive to internal pressure of the compressible fluidand/or the volume of the contained chamber according to variousthermodynamic principles (e.g. ideal gas law, Boyle's law, adiabaticcompression). In various embodiments, the stiffness of theextension-side accumulator 720 may be at least 5 times or at least 10times the stiffness of the compression-side accumulator 726. In certainembodiments, the compression-side accumulator may have a stiffnessbetween 1E10 Pa/m{circumflex over ( )}3 to 1E11 Pa/m{circumflex over( )}3, and/or the extension-side accumulator may have a stiffnessbetween 1E11-Pa/m{circumflex over ( )}3 to 1E12 Pa/m{circumflex over( )}3. Embodiments having values outside of these specific ranges arealso contemplated to be within the scope of the present disclosure.

Additionally or alternatively, as illustrated in FIG. 7, in certainembodiments a flow path fluidically coupling the compression chamber 706of the actuator 700 to the compression-side working chamber 738 a of thecompression-side accumulator 726 may be shorter (i.e., have a shorterlength) than a flow path fluidically coupling the compression chamber706 of the actuator 700 to the pump 718 (e.g., the compression-sidesecond flow path 730 may be shorter than the compression flow path 724,as is shown in FIG. 7). Additionally or alternatively, in certainembodiments, a flow path fluidically coupling the extension-side workingchamber 738 b of the extension-side accumulator 720 to the extensionchamber 704 of the actuator 700 may be shorter (i.e., have a shorterlength) than a flow path fluidically coupling the pump 718 to theextension chamber 704 of the actuator 700 (e.g., the extension-sidesecond flow path 701 may be shorter than the extension flow path 716, asis shown in FIG. 7).

Additionally or alternatively, in certain embodiments, at least one ofthe compression-side accumulator 726 and the extension-side accumulator720 may be a type-2 accumulator. Inventors have determined that, atleast for reasons similar to those discussed above, a hydraulic systemcomprising two accumulators wherein at least one of the accumulators isa properly configured and positioned type-2 accumulator may exhibitenhanced ripple attenuation between the pump and the actuator pistonover an extended frequency range, at least as compared to a similarsystem in which none of the accumulators are a type-2 accumulator.

FIG. 8 depicts an embodiment of a hydraulic system in which thecompression-side accumulator 726 is a type-2 accumulator, and theextension-side accumulator 720 is a type-1 accumulator. As can beobserved, in the illustrated embodiment the compression-side accumulator726 includes a first port 802 that allows fluid to ingress/egress thecompression-side working chamber 738 a of the compression-sideaccumulator 726 from/to the compression-side first flow path 728, and asecond port 804 that allows fluid to ingress/egress the compression-sideworking chamber 738 a of the compression-side accumulator 726 from/tothe compression-side second flow path 730, and may therefore beclassified as a type-2 accumulator. The illustrated extension-sideaccumulator 720, on the other hand, has only one port 735 b throughwhich fluid can ingress or egress the extension-side working chamber 738b of the extension-side accumulator 720 (that is, in the illustratedembodiment, the extension-side accumulator 720 is a type-1 accumulator).In certain embodiments, both the extension-side accumulator 720 andcompression-side accumulator 726 may be type-2 accumulators.

The inventors have recognized that overall system performance may dependon a first fluid impedance of the compression-side first flow path 728in comparison with a second fluid impedance of the compression-sidesecond flow path 730. Fluid impedance describes the resistance to fluidflow in a hydraulic system in response to a pressure difference betweentwo points in the system. Without wishing to be bound to any particulartheory, fluid impedance may be directly proportional to a value known asfluid inertance (sometimes referred to in the art as fluid inductance).Inertance of a flow path (and, therefore, impedance of the flow path) isdirectly proportional to density of the fluid occupying the flow path,an effective length of the flow path, and an effective cross sectionalarea of the flow path.

Without wishing to be bound to any particular theory, in the embodimentshown in FIG. 8, a first resonance frequency may be associated with pumpinduced displacement of fluid (e.g., due to pump ripple) in thecompression-side first flow path 728 interacting with fluid in thecompression-side accumulator 726. The first resonance frequency may beinversely related to a first inertance or first impedance of thecompression-side first flow path 728. Likewise, a second resonancefrequency may be associated with displacement of fluid in thecompression-side second flow path 730 interacting with fluid in thecompression-side accumulator 726. The second resonance frequency may beinversely related to a second inertance or second impedance of thecompression-side second flow path 730. If these two resonances havesimilar or overlapping frequencies, they may combine in a constructive,near constructive, unpredictable, and/or undesirable fashion.

To avoid undesired interactions between the flow paths, inventors havedetermined that, in certain applications, it may be preferable to designthe hydraulic system such that the compression-side first flow path 728has a first inertance and/or first impedance that is different than asecond inertance and/or second impedance of the compression-side secondflow path 730, such that a first resonance associated with displacementof fluid in the compression-side first flow path 728 between the pumpand compression side accumulator is spaced apart in frequency comparedto a second resonance associated with displacement of fluid in thecompression-side second flow path 730 between the compression sideaccumulator and the compression chamber. Particularly, inventors havedetermined that, in certain embodiments, systems in which thecompression-side second flow path 730 has a second inertance or secondimpedance less than the first inertance or first impedance of thecompression-side first flow path 728 may minimize undesirable rippletransfer while maintaining rapid response times. In certain embodiments,therefore, the flow paths and components may be configured andpositioned such that the compression-side first flow path 728 may have afirst inertance and/or a first impedance that is larger than a secondinertance and/or second impedance of the compression-side second flowpath 730. In certain embodiments, the first inertance and/or firstimpedance may be larger than the second inertance and/or secondimpedance by a factor of at least 5 or at least 10. In certainembodiments, the first inertance and/or first impedance may not exceed1000 times the second inertance and/or second impedance, respectively.In certain embodiments, the first inertance is between 1E6 to 1E7kg/m{circumflex over ( )}4, and the second inertance is between 1E5 to1E6 kg/m{circumflex over ( )}4. Embodiments having values outside ofthese specific ranges are also contemplated to be within the scope ofthe present disclosure.

As inertance is proportional to ρl/A (where ρ is density of fluid, l islength of the flow path, and A is cross sectional area of the flowpath), inertances (and, therefore, impedances and resonance frequencies)may be tuned by, for example, adjusting the relative lengths of thecompression-side first flow path 728 and compression-side second flowpath 730, and/or by adjusting a cross sectional area of thecompression-side first flow path 728 relative to the compression-sidesecond flow path 730. In certain embodiments, a first cross sectionalarea of a first portion of the compression-side first flow path 728and/or first port 726 may be smaller than a second cross sectional areaof a second portion of the compression-side second flow path 730 and/orsecond port 804, respectively. In certain embodiments, the second crosssectional area may be larger than the first cross sectional area by afactor of at least 2. In other embodiments, the second cross sectionalarea may be larger than the first cross sectional area by a factor of atleast 5. In certain embodiments, the first cross-sectional area may bebetween 10 mm and 100 mm, and the second cross-sectional area may bebetween 100 mm to 300 mm. Alternatively or additionally, as fluidinertance is proportional to length, the compression-side accumulator726 may be located such that the compression-side first flow path 728has a first length that is larger than a second length of thecompression-side second flow path 730. In certain embodiments, the firstlength may be larger than the second length by a factor of at least 1.5.Embodiments having values falling outside of the aforementioned specificranges are also contemplated to be within the scope of the presentdisclosure.

In some embodiments, the inertance or impedance of one or more of theflow paths may be adjusted or altered by incorporating one or moreinserts into the passage. Such an insert or inserts may be used tochange the effective cross-sectional flow area and/or shape of the flowpath over a portion or over the entire length of one or more flow paths.In this manner the configuration of the actuator system may be adjustedfor example, during tuning of a design during development.Alternatively, inserts may be used to tune production units to maintainconsistent performance in the field.

Since resonance frequency may be inversely related to the square root ofinertance, designing the system such that the first inertance and/orimpedance is larger than the second inertance and/or impedance mayresult in the first resonance frequency being lower (i.e., occurring ata lower frequency) than the second resonance frequency. As discussedpreviously, resonance frequencies may be represented as a local orglobal maximum in a plot of. For example, FIG. 13 depicts a first TFmag1302 of a first transfer function that describes the relationship ofpressure between a first point 850, located in the compression-sidefirst flow path 728 of FIG. 8, and a second point 852, located in theworking chamber 852 of the compression-side accumulator 726 of FIG. 8.As can be observed in FIG. 13, TFMag 1302 has a local maximum 1304(which, in the specific embodiment, also happens to be a global maximum)at a frequency 1306 (a “first frequency”) of approximately 15 Hz. FIG.13 further depicts a second TFmag 1301 of a second transfer functionthat describes the relationship of pressure between the second point 852and a third point 854 that is located in the compression chamber 706 ofthe actuator 700 of FIG. 8. As can be observed in FIG. 13, the secondTFmag 1301 has a local maximum 1303 (which, in the specific embodiment,also happens to be a global maximum) at a frequency 1305 (a “secondfrequency”) of 800 Hz. Since the second frequency 1305 is greater than(i.e., at a higher frequency than) the first frequency 1306, thissuggests that impedance or inertance of the compression-side first flowpath 728 in FIG. 8 is higher than impedance or inertance of thecompression-side second flow path 730.

In certain embodiments, therefore, a first TFmag of a first transferfunction describing a relationship between pressure at a first point850, located in the pump 718, a port of the pump 718, or in thecompression-side first flow path 728, and pressure at a second point852, located in the internal volume 732 a of the compression-sideaccumulator 726 (e.g., in the working chamber 738 a or the containedchamber 734 a), has a local and/or global maximum at a first frequency;and a second TFMag of a second transfer function describing arelationship between pressure at the second point 852 and pressure at athird point 854, located in the compression-side second flow path 730 orthe compression chamber 706 of the actuator 700, has a local and/orglobal maximum at a second frequency, wherein the second frequency ishigher than the first frequency. In certain embodiments, the firstfrequency is less than a first upper limit. In certain embodiments, thefirst upper limit may be 100 Hz, 90 Hz, 80 Hz, 60 Hz, 50 Hz, 30 Hz, 20Hz, 15 Hz, 10 Hz, or 5 Hz. Additionally or alternatively, in certainembodiments, the first frequency is greater than a first lower limit. Incertain embodiments, the first lower limit may be 0 Hz, 2 Hz, 5 Hz, or10 Hz. In certain embodiments, the first frequency is in the range of5-90 Hz. In certain embodiments, the second frequency is larger than asecond lower limit. In certain embodiments, the second lower limit is50, 100, 200, 300, 400, or 500 Hz. In certain embodiments, the secondfrequency is smaller than a second upper limit. In certain embodiments,the second upper limit is 800 Hz, 1000 Hz, or 1500 Hz. In certainembodiments, the second frequency is larger than the first frequency bya factor of at least 5. In certain embodiments, the second frequency islarger than the first frequency by a factor of at least 20. In certainembodiments, the second frequency is between 500 Hz-1000 Hz. Embodimentshaving values outside the aforementioned specifically stated ranges arealso contemplated to be within the scope of the present disclosure.

Alternatively or additionally, as discussed previously, resonancefrequencies of a hydraulic system may be determined by using a TFph of atransfer function. A TFph of a transfer function may have a value of+/−90° for pressure pulsations having a frequency corresponding to aresonance frequency of the system. For example, FIG. 14 illustrates afirst TFph 1402 of a first transfer function describing a relationshipbetween pressure at a first point 850 that is located in thecompression-side first flow path 728 of FIG. 8 and pressure at a secondpoint 852 that is located in the working chamber 852 of thecompression-side accumulator 726. As can be seen from FIG. 14, the firstTFph 1402 has a value of −90° 1404 at a first frequency 1406 ofapproximately 15 Hz. FIG. 14 further depicts a second TFph 1401 of asecond e transfer function describing the relationship between pressureat the second point 852 and pressure at a third point 854 that islocated in the second flow path 854 of FIG. 8. As can be seen from FIG.14, the second TFph 1401 has a value of −90° 1403 at a second frequency1405 of 800 Hz. As the second frequency 1405 is larger than the firstfrequency 1406, this indicates that a first inertance or first impedanceof the compression-side first flow path 728 is larger than a secondinertance or second impedance of the second flow path 854.

Therefore, instead of (or in addition to) using TFmag of varioustransfer functions to determine various resonance frequencies, it may bepossible to determine the aforementioned first frequency and/or secondfrequency using TFph of the v transfer functions. TFph may be obtainedby, for example, introducing pressure waves of various frequencies intoa hydraulic system, and then detecting (for example, using pressuresensors) the phase of the pressure wave at various points in thehydraulic system.

In certain embodiments a TFph of a first transfer function describing arelationship between pressure at a first point 850, located in the pump718, a port of the pump 718, or in the compression-side first flow path728, and pressure at a second point 852, located in the internal volume732 a of the compression-side accumulator 726 (e.g., in the workingchamber 638 a or the contained chamber 634 a), has a value of +/−90° ata first frequency, while a second TFph of a second transfer functiondescribing a relationship between pressure at the second point 852 andpressure at the third point 854, located in the compression-side secondflow path 730 or the compression chamber 706 of the actuator 700, has avalue of +/−90° at a second frequency. In certain embodiments, thesecond frequency is higher than the first frequency. In certainembodiments, the first frequency is less than a first upper limit. Incertain embodiments, the first upper limit may be 50 Hz, 100 Hz, 80 Hz,60 Hz, 50 Hz, 30 Hz, 20 Hz, 15 Hz, 10 Hz, or 5 Hz. Additionally oralternatively, in certain embodiments, the first frequency is greaterthan a first lower limit. In certain embodiments, the first lower limitmay be 0 Hz, 2 Hz, 5 Hz, or 10 Hz. In a preferred embodiment, the firstfrequency is in the range of 10-50 Hz. In certain embodiments, thesecond frequency is larger than a second lower limit. In certainembodiments, the second lower limit is 50 Hz, 100, 200, 300, 400, or 500Hz. In certain embodiments, the second frequency is smaller than asecond upper limit. In certain embodiments, the second upper limit is800 Hz, 1000 Hz, or 1500 Hz. In certain embodiments, the secondfrequency is larger than the first frequency by a factor of at least 5.In a preferred embodiment, the second frequency is between 500 Hz-1000Hz. Embodiments having values outside the aforementioned specificallystated ranges are also contemplated to be within the scope of thepresent disclosure.

Having discussed a first resonance frequency and a second resonancefrequency, a third resonance frequency may be considered that isassociated with interaction of fluid in the extension-side accumulator720 and fluid in the extension flow path 716 or a portion thereof. Forreasons described above, inventors have recognized that it may bedesirable to design the extension-side accumulator such that the thirdfrequency does not overlap with, and is sufficiently different from, thefirst frequency and/or the second frequency. Spacing out the resonancefrequencies as described is preferable since it minimizes the risk ofone resonance unpredictably and/or undesirably exciting anotherresonance in the system. In an embodiment, the extension-sideaccumulator may be configured and positioned such that the thirdresonance frequency is greater than the first frequency and less thanthe second frequency. The third resonance frequency may be adjusted bytuning the size of the extension-side accumulator 720 (e.g., the size ofits internal volume 732 b), a length of a neck 801 of the extension-sideaccumulator 720, and/or a cross sectional area of the neck 801. Incertain embodiments, the neck 801 has a diameter between 4 mm and 10 mm,and a length less than 5 mm. In certain embodiments, a ratio of thediameter of the neck 801 over the length of the neck 801 is at least0.8.

In certain embodiments, a third TFmag of a third transfer functiondescribing a relationship between pressure at a fourth point 856,located in the extension flow path 716, pump 718, or a port of the pump718, and pressure at a fifth point 858, located in the either (a) theextension-side working chamber 738 b of the extension-side accumulator720 or (b) the contained chamber 734 b of the extension-side accumulator720, may have a local or global maximum at the third frequency.Alternatively or additionally, in certain embodiments a third TFph ofthe third transfer function may be equal to +/−90° at the thirdfrequency. In certain embodiments, the third frequency is greater thanthe first frequency and/or less than the second frequency. In certainembodiments, the third frequency is greater than the first frequency bya factor of at least 2, at least 5, at least 10, at least 15, at least20, or at least 25. In certain embodiments, the third frequency is atleast 100 Hz. In certain embodiments, the third frequency is below 500Hz. Embodiments having values outside the aforementioned specific rangesare also contemplated to be within the scope of the present disclosure.

FIG. 9 shows an additional embodiment of the hydraulic system that issimilar to that of FIG. 8, with the exception that the extension-sideaccumulator 720 of FIG. 9 is a type-2 accumulator, characterized bycomprising two distinct ports—(i) a third port 902 a and (ii) a fourthport 902 b—through which fluid may ingress/egress the working chamber904 of the extension-side accumulator 720 to/from the extension flowpath 716 (shown with diagonal hatch marks). As illustrated, theextension flow path 716 comprises (a) the extension-side first flow path722 that fluidically couples the pump 718 to the extension-side workingchamber 904 of the extension-side accumulator 720, and (b) theextension-side second flow path 701 that fluidically couples the workingchamber 904 of the extension-side accumulator 720 to the extensionchamber 704 of the actuator 700. The extension-side first flow path 722may be characterized as having a third length, third impedance, and/orthird inertance. Likewise, the extension-side second flow path 701 maybe characterized as having a fourth length, fourth impedance, and/orfourth inertance.

For reasons set forth above with regard to the compression-sideaccumulator, in embodiments with a type-2 extension-side accumulator720, the system may be configured such that a third resonance frequencyassociated with the extension-side accumulator 720 interacting withfluid in the extension-side first flow path 722 is spaced apart from afourth resonance frequency associated with the extension-sideaccumulator 720 interacting with fluid in the extension-side second flowpath 701. As discussed above, this can be accomplished by tuning theinertances (e.g., by tuning lengths and/or cross-sectional areas of atleast portions of each flow path) of the extension-side first flow path722 and extension-side second flow path 701. In certain embodiments, thethird length is larger than the fourth length. In certain embodiments,the third impedance and/or third inertance is/are larger than the fourthimpedance and/or fourth inertance, respectively. In various embodiments,the third inertance is larger than the fourth inertance by a factor ofat least 5× or at least 10×. In various embodiments, a fourth crosssectional area of a fourth portion of the extension-side second flowpath is larger than a third cross sectional area of a third portion ofthe extension-side first flow-path. In various embodiments, the fourthcross sectional area is larger than the third cross-sectional area by afactor of at least 2; in certain embodiments, the fourth cross sectionalarea is larger than the third cross-sectional area by a factor of atleast 5.

In an automotive suspension application, a plurality of distributedhydraulic actuators may be utilized (e.g., in conjunction with, forexample, a plurality of springs) to mechanically couple a wheel or wheelassembly of a vehicle to a body of the vehicle. FIG. 10 depicts anembodiment of a vehicle comprising a vehicle body 1002 and a pluralityof wheels 1004 a-b. In certain embodiments, the vehicle may comprise aplurality of hydraulic actuators 700 a-b, with each actuatormechanically coupling each wheel 1004 a-b to a portion of the vehiclebody 1002. Such an active suspension system may allow for the distancebetween the vehicle body 1002 and each wheel 1004 a-b to beindependently adjusted. In current commercially available,hydraulic-based active suspension systems, two or more actuators 700 a-butilize a common, centralized pump and/or a common, centralized set ofaccumulators. Free space or free volume near a wheel 1004 a-b is highlylimited; therefore, locating a common, shared pump in a central locationthat is remote from the wheels 1004 a-b may reduce size constraints onthe pump.

Returning now to FIG. 8, in some embodiments, locating the pump 718 in acentralized location remote from the actuator 700 may necessitate arelatively long compression flow path 724 (indicated by horizontal hatchmarks) and/or extension flow path 716 (indicated by diagonal hatchmarks). Inventors have recognized that such long flow paths may degraderesponse time such that the system is not able to respond fast enough tocertain vehicle events (such as driving over bumps, potholes, turning,braking, etc.). Accordingly, inventors have determined that, in certainembodiments, response time may be significantly improved over currentcommercially available active suspension systems by minimizing a lengthof the compression flow path 724 and/or extension flow path 716. Incertain embodiments, the length of the compression flow path 724 and/orextension flow path 716 may be less than a length 709 of the actuatorhousing 702. In certain embodiments, the sum of the length of thecompression flow path 724 and the length of the extension flow path 716may be less than the length 709 of the actuator housing 602. Theserelatively short flow paths may be achieved by locating individual pumpsand accumulators in each wheel well, such that each actuator 700 isassociated with its own local pump 718, compression-side accumulator726, and extension-side accumulator 720. Therefore, in certainembodiments, a vehicle includes a plurality of wheels, each wheellocated in a wheel well, wherein each wheel well includes a localizedactuator 700, a localized pump 718, a localized compression-sideaccumulator 726, and a localized extension-side accumulator 720. Theseembodiments may optimize response time, but may require more space sincehydraulic components are localized at the wheel well rather than beingremotely located. In other embodiments, in which space constraints areprioritized over response time, two or more actuators 700 a-b may sharea common, centralized pump 718, a common centralized compression-sideaccumulator 726, and/or a common centralized extension-side accumulator720. The improved performance as described with reference to FIG. 8 mayalso be achieved with the embodiments illustrated in FIGS. 7, 9-11and/or described herein.

In order to minimize the length (and, therefore, inertances) of one ormore flow paths, a housing 733 a of the compression-side accumulator 720and/or housing of the extension-side accumulator may share one or morecommon components (e.g., one or more common walls) with the actuatorhousing 702. Alternatively or additionally, in certain embodiments, thehousing 733 a of the compression-side accumulator and/or housing of theextension-side accumulator may be directly attached to the actuatorhousing 702.

FIG. 11A illustrates an embodiment of a hydraulic system similar to thatof FIG. 8, wherein the housing 733 a of the compression-side accumulator720 and the actuator housing 702 share at least one common wall 1101. Inthe illustrated embodiment, the length of the compression-side secondflow path 730 is minimized, such that the length corresponds only to thethickness of the wall of the actuator housing 702. Likewise, in certainembodiments the housing 733 b of the extension-side accumulator 720 andthe actuator housing 700 may share at least one common portion. Incertain embodiments, the housing 733 b of the extension-side accumulator720 may be directly attached to the actuator housing 700. In certainembodiments, the extension-side accumulator 720 may be integrated intothe pump 718, such that a housing of the pump 718 and the housing 733 bof the extension-side accumulator 720 share at least one common portion.

Given the space constraints of a vehicle, especially of a wheel well ofa vehicle, in certain embodiments it may be desired to locate the pump718 and at least one of the compression-side accumulator 726 or theextension-side accumulator 720 on opposing sides of the actuator 700.FIG. 11B illustrates an embodiment in which the pump 718 andextension-side accumulator 720 are located on a first side of theactuator 700 and the compression-side accumulator 726 is located on asecond side of the actuator 700. The compression flow path (shown indark gray and light gray fill) includes the compression-side first flowpath 728, which fluidically couples the pump 718 to the compression-sideworking chamber 738 a of the compression-side accumulator 726 is shownin light gray; and the compression-side second flow path 730, whichfluidically couples the compression-side working chamber 738 a of thecompression-side accumulator 726 to the compression chamber 706 of theactuator 700 is shown in dark gray. The hydraulic system furtherincludes the extension flow path 716 (shown with gray diagonal lines),which fluidically couples the pump 718 to the extension chamber 704 ofthe actuator 700. Dotted arrows indicate how fluid communication mayoccur.

In certain embodiments, the hydraulic system may include one or moreannular cavities that at least partially encompass the actuator housing.An annular cavity is understood to mean a fluid filled volume at leastpartially bounded by two concentric ellipses (e.g., circles) or arcuateportions thereof. Utilizing such annular flow paths potentially allowsfor more compact and/or lightweight packaging, since such a designallows the actuator housing itself to serve multiple functions by both(i) at least partly defining the compression chamber or extensionchamber of the actuator, as well as (ii) at least partly defining one ormore annular cavities. These annular cavities may be formed by one ormore outer housings or outer housings that at least partially surroundthe actuator housing 702, such that a gap or cavity exists between theouter housing or outer housing and an outer surface of actuator housing702.

In other embodiments, the hydraulic system may include a plurality ofannular cavities. As can be seen, the extension flow path (shown withdiagonal hatch marks) includes first outer cavity 1150 (e.g., an annularor semi annular cavity) that encircles at least a portion of theextension chamber 704 and/or compression chamber 706. Likewise, thecompression flow path (shown with dark gray and light grey fills)includes a second outer cavity 1160 (e.g., an annular or semi-annularcavity). In other embodiments, the hydraulic system may include only asingle annular cavity (e.g., the first outer cavity 1150). In certainembodiments, a portion of at least one of, at least two of, at leastthree of, or at least four of the group consisting of (i) thecompression-side first flow path 728, (ii) the compression-side secondflow path 730, (iii) the extension-side first flow path 722, and (iv)the extension-side second flow path 701 is/are partly defined by theactuator housing 702 (e.g., the flow paths may include a cavity that isbounded on at least one side by a portion of the actuator housing 720).In certain embodiments, at least one of, at least two of, at least threeof, or at least four of the aforementioned group of flow paths mayinclude an annular or semi annular cavity that at least partiallyencircles at least a portion of the actuator housing 702.

In certain embodiments, the annular cavity (such as, for example, thefirst outer cavity 1150) may be utilized to create a flow path (e.g., anextension flow path, shown by diagonal hatch marks) that, at least atportions, has a length much larger than a gap forming the annular cavity(e.g., the gap between the outer surface of the actuator housing 702 andthe inner surface of the first outer housing 1170, or the gap betweenthe first outer housing 1170 and the second outer housing 1180). Suchflow paths may exhibit a pressure drop vs. flow rate relationship that,at least for certain flow rates, behaves linearly. Further, the fluidinertance introduced by such a flow path may allow for fluid in theannular cavity or a portion thereof to interact with a compliance offluid in the surrounding volumes to introduce an additional resonancefrequency. Due in part to this additional resonance, pressure pulsationshaving frequencies higher than this additional resonance frequency maybe attenuated during propagation from the pump 718, through the annularcavity (e.g., the first outer cavity 1150), and to the actuator (e.g.,the extension chamber 704 of the actuator). In certain embodiments, theadditional resonance frequency falls in a range between 150 Hz to 250 HzIn the illustrated embodiment of FIG. 11B, the first outer cavity 1150has an annular cross section that is bound by an outer surface of theactuator housing 702 and the inner surface of a first outer housing 1170that encircles at least a portion of actuator housing 702. Inventorshave recognized that, at least for embodiments in which the actuatorhousing 702 and first outer housing 1170 are cylindrical, inertances(which depend on cross-sectional area of a flow path, as describedabove) and/or restrictions in the first outer cavity 1150 may beadjusted by changing an inner diameter of the first outer housing 1170relative to an outer diameter of the actuator housing 702, such that thecross-sectional area of the first outer cavity 1150 is varied.

Likewise, in the illustrated embodiment of FIG. 11B, the second outercavity 1160 has an annular cross section that is bound by an outersurface of the first outer housing and an inner surface of a secondouter housing 1180 that encircles at least a portion the first outerhousing. At least for embodiments in which the first outer housing 1170and second outer housing 1180 are cylindrical, inertances (which dependon cross-sectional area of a flow path, as described above) and/orrestrictions in the second outer cavity 1160 may be adjusted by changingan inner diameter of the second outer housing 1180 relative to an outerdiameter of the first outer housing 1170, such that the cross-sectionalarea of the second outer cavity 1160 is varied.

In certain embodiments, a sleeve (not pictured) may be inserted into atleast portion of one of the annular cavities (e.g., into the first outercavity 1150 and/or second outer cavity 1160), thereby reducing the gapbetween the actuator housing 702 and the first outer housing 1170, orthe gap between the first outer housing 1170 and the second outerhousing 1180. In certain embodiments, the sleeve may be in physicalcontact with at least a portion of the outer surface of the actuatorhousing 702. In certain embodiments, the sleeve may be in physicalcontact with at least a portion of a surface of the first outer housing.In certain embodiments, the sleeve may be in physical contact with atleast a portion of a surface of the second outer housing. The thicknessof the sleeve may be controlled in order to vary the annularcross-sectional area of the annular cavity, thereby allowing for controlof various properties (e.g., inertance, impedance, restriction).

In certain embodiments, the difference of the inner diameter of thefirst outer housing 1170 and the outer diameter of the actuator housing702 may be greater than 0.4 mm and less than 1 mm. In certainembodiments, the difference of the inner diameter of the first outerhousing 1170 and the sum of the outer diameter of the actuator hosing702 and the thickness of a sleeve inserted into the first outer cavity1150 may be greater than 0.4 mm and less than 1 mm. In certainembodiments, the length of the first outer cavity 1150 may be largerthan 50 mm and less than 100 mm. For all ranges given above, alternativeembodiments having values falling outside of the exact stated ranges maybe envisioned that are within the scope of this disclosure.

FIG. 26 illustrates two TFmags of two pressure/pressure transferfunctions from two different hydraulic systems of the type shown in FIG.11b . The only difference between the two systems was the annularcross-sectional area of the first outer cavity 1150. Particularly, theannular cross-sectional area (and therefore inertance and impedance) ofthe first outer cavity 1150 was adjusted by inserting a sleeve into thefirst outer cavity 1150. Each pressure/pressure transfer functiondescribes a relationship between pressure at the pump 718 and pressureat a point in the extension chamber 704 in the respective hydraulicsystem. As can be seen by comparing the two TFmags in FIG. 26, tuning ofthe cross-sectional area (and therefore inertance and impedance) of thefirst outer cavity 1150 may significantly improve attenuation capabilityof the system.

The illustrated embodiment of FIG. 11b further includes an annular dam1101 a-b that divides the outer annular cavities 1160 into an uppersection 1162 (that is part of the compression-side first flow path 728)and a lower section 1164 (that is part of the compression-side secondflow path 730). The annular dam serves as a barrier that separates fluidin the upper section 1162 of the outer annular cavity 1160 from fluid inthe lower section 1164 of the outer annular cavity 1160. In certainembodiments, the inner cavity 1150 may include one or more annular damsthat divide the inner cavity 1150 into various sections. In certainembodiments, the annular dams 1101 a-b are elastomeric or rubbero-rings.

In certain embodiments, one or more components may share a commonhousing with the pump. This type of packaging may allow for more compactsystems and/or may reduce the number of welds or other attachments. Forexample, as shown in FIG. 11B, the pump 718 and/or extension-sideaccumulator 720 may be encased in a common pump housing 1110.

In certain embodiments in which the extension-side accumulator is atype-1 accumulator, the extension-side accumulator 720 may be locatedsuch that the extension-side first flow path is shorter and/or has aninertance less than the extension side second flow path 701. In certainembodiments, as shown, the pump housing 1110 may overlap with a portionof the actuator housing 702, such that the two housings share a commonwall or structural member. In certain embodiments, the pump housing 1110may be directly attached to at least a portion of the actuator housing702. In certain embodiments, as shown in FIG. 11B, the extension-sideaccumulator 726 may comprise an accumulator piston 1150 having a firstsurface 1152 exposed to fluid in the compression-side working chamber738 a of the extension-side accumulator 726. In certain embodiments, afirst direction 1154 that is normal to the first surface 1152 of theaccumulator piston 1150 may be parallel to a second direction 1156 thatis normal to the first face 710 of the piston 708 of the actuator 700.

As described above, various inertances of respective flow paths in ahydraulic system may impact overall system performance in a variety ofmetrics. As inertance depends, in part, on both the length and/orcross-sectional area of a flow path or portion thereof, varying one ormore inertance in the hydraulic system in some cases may requiresubstantial redesign (e.g., relocation of various components) of theoverall system. Such redesign in turn may require re-toolingmanufacturing equipment, resulting in extended turnarounds toaccommodate the changes. Therefore, inventors have recognized that itmay be beneficial to design a type-2 accumulator such that inertances ofthe various flow paths into/out of the working chamber of theaccumulator may be adjusted without requiring redesign of the overallhydraulic system (e.g., relocation of various components).

FIG. 12A-12C depict various embodiments of type-2 accumulators in whichvarious inertances may be adjusted by adjusting design parameters of theaccumulator, such that redesign of an overall hydraulic system may notbe required. FIG. 12A depicts one embodiment of a type-2 accumulator. Inthe illustrated embodiment, the accumulator 1200 includes a cylindricalhousing 733 defining an internal volume. In various embodiments, thehousing 733 and/or internal volume may have any geometry (e.g.,spherical, cubical, cuboidal, etc.). In certain embodiments, a piston736 (or other barrier, e.g. a bladder) inserted into the internal volumeseparates fluid (e.g., gas) in a contained chamber 734 from fluid (e.g.,hydraulic fluid) in a working chamber 738. As shown in the illustratedembodiment, the housing 733 defines an opening 1202 therethrough, theopening having a first area. A tube 1204 having a wall defining a bore1206 may be inserted into the opening 1202, such that at least a portionof the outer surface of the wall of the tube 1204 is exposed to fluid inthe working chamber 738. A cross-sectional area of the tube 1202 isunderstood to include a cross-sectional area of the bore 1206 plus across-sectional area of the solid wall encircling (or otherwisedefining) the bore 1206. In various embodiments, the wall of the tubemay be flexible or rigid, as the disclosure is not so limited. Invarious embodiments, the tube wall may be a metal, a ceramic, a plastic,or a combination thereof.

Continuing with FIG. 12A, since the cross-sectional area of the tube1204 is less than the first area of the opening 1202, a free spaceexists around the wall of the tube 1204 through which fluid mayingress/egress (as shown by dotted arrows) the working chamber 738.Fluid may also ingress/egress (as shown by dotted arrows) the workingchamber 738 by passing through the bore 1206 of the tube 1204. The freespace around the wall of the tube 1204 may be in direct fluidcommunication (via, for example, a hose or pipe) with a hydraulic systemat one point, while the bore 1206 of the tube 1204 may be in directfluid communication with the hydraulic system at another point. Theaccumulator 1200 therefore includes two distinct, non-overlapping paths(e.g., through the free space around the tube 1204, and through the bore1206 of the tube 1204) into which fluid may ingress/egress the workingchamber 738, and may therefore be classified as a type-2 accumulator.

The embodiment of the accumulator illustrated in FIG. 12A, or variantsthereof, may be integrated into any of the previously describedhydraulic systems that include a type-2 accumulator. For example, theaccumulator shown in FIG. 12A may be integrated into the hydraulicsystem of FIG. 8 as the compression side accumulator 726, in which casethe bore 1206 of the tube 1204 may be in direct fluid communicationwith, for example, the compression-side second flow path 730 and thefree space around the tube 1204 may be in direct fluid communicationwith, for example, the compression-side first flow path 728 (or viceversa).

Advantageously, inertances or impedances of various flow paths into/outof the working chamber 738 of the accumulator shown in FIG. 12A may betuned without requiring redesign or relocation of the overall hydraulicsystem. Particularly, impedances and/or inertances may be controlled byadjusting the cross sectional area of the opening 1202, thecross-sectional area of the tube 1204, the cross-sectional area of thebore 1206 of the tube 1204, and/or the thickness of the wall of thetube. These parameters in turn may be adjusted by modifying a diameterof the opening 1202, an outer diameter of the wall of the tube 1204,and/or an inner diameter of the wall of the tube 1204. Inertance offluid in the bore 1206 of the tube 1204 may further be adjusted bymodifying the length of the tube 1204. In certain embodiments, theopening 1202 is circular and the tube 1204 has a circular cross section,in which case any free space surrounding the tube 1204 is annular.However, in other embodiments the opening 1202, the second opening 1208,the tube 1206, and the free space around the tube 1206 may have anycross sectional geometry, as the disclosure is not so limiting.

FIG. 12B illustrates another embodiment of a type-2 accumulator, whereinthe tube 1204 is inserted through a first opening in the accumulatorhousing 733, and the accumulator comprises a second opening 1208 throughthe accumulator housing 733. In certain embodiments, the second opening1208 may be through a side or base of the accumulator housing 733. Theembodiment of the accumulator illustrated in FIG. 12B may be integratedinto any of the previously described hydraulic systems that include atype-2 accumulator. For example, the accumulator shown in FIG. 12b , orvariants thereof, may be integrated into the hydraulic system of FIG. 8as the compression side accumulator 726, in which case the bore 1206 ofthe tube 1204 may be in direct fluid communication with, for example,the compression-side second flow path 730 and the second opening 1208may be in direct fluid communication with, for example, thecompression-side first flow path 728 (or vice versa).

Advantageously, inertances or impedances of various flow paths into/outof the working chamber 738 of the accumulator shown in FIG. 12B may betuned without requiring redesign or relocation of the overall hydraulicsystem. Particularly, inertances and/or impedances may be controlled byadjusting the diameter or cross sectional area of the opening 1208, thediameter or cross-sectional area of the bore 1206 of the tube 1204,and/or the length of the tube 1204. In certain embodiments, both thesecond opening 1208 and the cross section of the bore 1206 of the tube1204 are circular 1208. However, in other embodiments the second opening1208 and/or the bore 1204 of the tube 1206 may have any cross sectionalgeometry, as the disclosure is not so limiting.

FIG. 12C illustrates yet another embodiment of a type-2 accumulator. Inthe illustrated embodiment, the accumulator comprises a first tube 1204having a wall defining a first bore 1206. As shown in FIG. 12C, thefirst tube 1204 may be inserted into a first opening through theaccumulator housing 733, such that at least a portion of an outersurface of the wall of the tube 1204 is exposed to fluid in the workingchamber 738. In the illustrated embodiment, the accumulator housing 733comprises a second opening 1208 therethrough, through which a secondtube 1210 having a second bore 1207 has been inserted such that at leasta portion of the outer surface of the wall of the second tube 1210 isexposed to fluid in the working chamber 738 of the accumulator 733. Incertain embodiments, as shown, the first tube 1204 and second tube 1210may be inserted at different angles relative to a direction normal to asurface of the barrier 736 exposed to fluid in the working chamber 738.In certain embodiments, the difference may be greater than 0° and lessthan 90°. In certain embodiments, as illustrated in FIG. 12C, both tubesmay be inserted through the side of the accumulator housing; in otherembodiments, one of the first tube 1204 and second tube 1210 may beinserted through a side of the accumulator housing 733 and the othertube may be inserted through a base of the accumulator housing 733; inyet other embodiments, both the first tube 1204 and second tube 1210 maybe inserted through the base of the accumulator housing 733.

Continuing with FIG. 12C, two distinct, non-overlapping paths existthrough which fluid may ingress/egress the working chamber 738—(i)through the first bore 1206 of the first tube 1204, and (ii) through thesecond bore 1207 of the second tube 1210. The illustrated embodiment maytherefore be considered a type-2 accumulator. The embodiment of theaccumulator illustrated in FIG. 12c may be integrated into any of thepreviously described hydraulic systems that include a type-2accumulator. For example, the accumulator shown in FIG. 12c may beintegrated into the hydraulic system of FIG. 11b as the compression sideaccumulator 726, in which case the bore 1206 of the first tube 1204 may,for example, make-up a portion of the compression-side first flow path728 (shown in light gray shading) and the bore 1207 of the second tube1210 may, for example, make-up a portion of the compression-side secondflow path 730.

Advantageously, inertances or impedances of various flow paths into/outof the working chamber 738 of the accumulator shown in FIG. 12c may betuned without requiring redesign or relocation of the overall hydraulicsystem. Particularly, inertances and/or impedances may be controlled byadjusting the length of the first tube 1204, the length of the secondtube 1210, the diameter or cross-sectional area of the first bore 1206of the first tube 1204, and/or the diameter or cross-sectional area ofthe second bore 1207 of the second tube 1210. In certain embodiments, asecond cross sectional area of the second bore 1207 is larger than afirst cross sectional area of the first bore 1206. In certainembodiments, the second cross sectional area is larger than the firstcross sectional area by a factor of at least 2. In certain embodiments,the second cross sectional area is larger than the first cross sectionalarea by a factor of at least 5. Alternatively or additionally, the firsttube 1204 may have a first length that is greater than a second lengthof the second tube 1210. In certain embodiments, the first length islarger than the second length by a factor of at least 5. In certainembodiments, the first length is larger than the second length by afactor of at least 10. Inventors have found that the aforementionedratios may result in hydraulic systems, such as that of FIG. 11b ,having the desired relative inertances described elsewhere in thisdisclosure.

Evaluations and Examples

For purposes of descriptive clarity, the fluid passages in variousschematic and diagrammatic illustrations herein are sometimes depictedas simple channels having a given length and cross section from whichfluid inertance can be reasonably predicted for approximate modellingand design. Further, in evaluating the various hydraulic systemsdescribed herein, various flow paths of the hydraulic system may betreated as an interconnected combination of individual inertanceelements and compliance elements. For example, the simple hydraulicsystem of FIG. 19a may be considered a combination of the elements asshown in FIG. 23, in which compliance elements have been depicted withdiagonal hatch marks and inertance elements depicted with horizontalhatch marks. Further, as would be understood by one of ordinary skill,inertance elements may be described by a mass and associated pressureareas, and compliant elements may be described by a volume andassociated stiffness. Modifications to the theoretical model shown inFIG. 23 which describe the various additional embodiments describedherein may be based on a combination of known fluid mechanicalprinciples and empirical testing.

As a result of empirical tests and evaluations of empirically andanalytically derived models, inventors have recognized that integratedhydraulic systems, understood to refer to hydraulic systems in whichmultiple components may be integrated into common housings or otherwiseclosely-coupled, may be complex and/or it may be difficult to predictbehavior and/or properties using a priori information. For example, inthe integrated or highly closely-coupled systems described herein,rather than each hydraulic component behaving as an independentfunctional element connected by long lengths of hose or pipe, thevarious components in a closely coupled systems are prone to interactwith each other in complex ways that can be advantageous (“synergistic”)or disadvantageous (“anti-synergistic”). For example, as will be shownherein, for those disclosed hydraulic systems comprising two distinctaccumulators, interactions may arise between the two accumulators thatmay be synergistic and thus advantageous (e.g., the two accumulators mayinteract in a way such that pulsations are attenuated to a level beyondthe simple vector sum of each accumulator's attenuation capability atany given frequency), or interactions may arise that areanti-synergistic and therefore disadvantageous (e.g., the combination oftwo accumulators may interact such that the total pulsation attenuationmay be less than the attenuation of a system having only one of the twoaccumulators). For example, oscillations in one accumulator may excitenatural frequencies in another accumulator.

Inventors have also determined, for example, that, among other factors,the relative location of each accumulator (relative to the pump and/orthe actuator) can significantly affect whether certain interactions aresynergistic or anti-synergistic.

In another consideration, further complexities are brought to bear withthe recognition that various features and properties of an actuatorsystem may influence the response time of a given hydraulic actuatorsystem. Properties that may influence response time include, forexample, moment of inertia of the motor, rod mass, compliances ofvarious elements, and the sum of inertances in each flow path throughoutthe hydraulic system. For example, in the case of modifying a hydraulicsystem having a type-1 accumulator to allow for incorporation of atype-2 accumulator, one or more additional flow paths may be included toadd to the overall fluid inertance of the system, thereby negativelyaffecting response time. For certain applications in which response timemay be a critical system metric, such modification to incorporate atype-2 accumulator may appear to be undesirable, especially if thevarious inertances of the flow paths are not carefully considered duringincorporation of the type-2 accumulator.

As the size of a hydraulic system is reduced (for example, to reducepackaging dimensions or to improve response times), components maybecome more closely integrated and their interactions more complex.Inventors have observed surprisingly large synergistic and/oranti-synergistic interactions in designs that, based purely on a priorievaluation, would not be expected.

Further, highly dynamic components such as a bidirectional high speedpump (in which a single side of the pump may at times serve as thedischarge side and at other times serve as the suction side) capable ofoperating over a wide range of speeds (and therefore, generatingpulsations at a wide range of frequencies) add to system complexity.

Returning again to FIG. 7, as previously discussed, pressure pulsationsmay be generated at a pump 718 due to pump ripple which may beundesirably transferred into force ripple, which is understood to referto pulsations in net force applied to the piston 708 of the actuator700. The net force applied to the piston 708 depends on the differenceof pressure of fluid in the compression chamber 706 (referred to hereinas T1′) and pressure of fluid in the extension chamber 704 (referred toherein as T2′). This pressure difference is referred to herein as ‘dP’,and can be thought of mathematically as P2−P1 (or the pressure of fluidin the extension chamber (P2) minus the pressure of fluid in thecompression chamber (P1)). Therefore, as recognized by the inventors,force ripple may result from pulsations in dP. Pulsations in dP may inturn result from variations of either P2 or P1, or from variations inboth P2 and P1. That is, the inventors have determined that even ifripple in P2 is eliminated (indicating complete attenuation of pressurepulsations between the pump 718 and the extension chamber 704 of theaccumulator 700), ripple in P1 are sufficient to result in pulsations indP and, therefore, undesirable force ripple. Likewise, even if ripple inP1 is completely eliminated (indicating complete attenuation of pressurepulsations between the pump 718 and the compression chamber 706 of theactuator 700), ripple in P2 are sufficient to result in pulsations in dPand, therefore, undesirable force ripple.

The aforementioned ripple phenomenon is demonstrated in FIGS. 16a -22,as described in detail herein. FIGS. 16a-22a each illustrate examples ofhydraulic systems, while FIGS. 16b-22b illustrate TFmags ofpressure/displacement transfer functions describing relationshipsbetween pulsations originating at a pump 718 and pulsations of dP acrossthe piston. The TFmags in the evaluated examples are plotted using a logscale on both axes, with the y-axis representing a log ratio ofamplitude of pulsations in dP divided by amplitude of the displacementripple generated at the pump, and the x-axis representing frequency ofthe displacement ripple generated at the pump. The illustrated TFmags ofthe transfer functions of 16 b-22 b were determined using an empiricallybased, customized lumped elements fluid dynamic model.

FIG. 16b illustrates behavior of dP in response to pump ripple in thesystem shown schematically in FIG. 16a , in which no accumulator isutilized. As can be seen from the relatively flat portion of FIG. 16b ,displacement ripple generated at the pump results in pulsations in dPacross the piston 708 regardless of frequency. Such behavior may arisesince, due to the lack of substantial compliance (such as would beprovided by an accumulator) in both the compression flow path 724 andextension flow path 716, pulsations can propagate from the pump nearlyunattenuated through both the compression flow path 724 and theextension flow path 716. It is noted that a resonance peak occurs atapproximately 920 Hz and that this peak causes amplification as opposedto attenuation of the amplitude of pulsations in dP. Without wishing tobe bound to theory, the peak may arise due to a Helmholtz-type resonancethat occurs between a fluidic inertance and an associated compliance.

As complexity of the system is increased by addition of accumulators,various additional resonances may arise within the frequency range ofthe plots. As was discussed previously, inventors have recognized that,in certain embodiments, configuring the system to avoid overlap or nearoverlap of frequencies of various resonances may reduce the likelihoodof anti-synergistic interactions.

In FIG. 17a , a type-1 accumulator 1701 is in fluid communication withthe compression flow path 724 fluidically coupling the pump 718 andcompression chamber 706. FIG. 17b illustrates the frequency dependentbehavior of dP in response to displacement ripple generated at the pumpin the system of FIG. 17a . While at lower frequencies there is somemodest attenuation of dP, above frequencies of approximately 50 Hz theTFmag approaches and even exceeds zero for certain ranges offrequencies, indicating no attenuation (and even possibly amplification)of pulsations at these frequencies. As discussed previously, theaddition of an appropriately sized accumulator on the compression sideattenuates pressure pulsations during propagation from the pump throughthe compression flow path 724. However, as there is no accumulator onthe extension side, pulsations may propagate nearly unattenuated throughthe extension flow path 716, resulting in pulsations in dP asillustrated.

FIG. 18a depicts a system with only one type-1 accumulator located onthe extension side (e.g., in direct communication with the extensionflow path 716). As can be seen in FIG. 17b , the behavior of the systemof FIG. 17a closely matches that of FIG. 16a since, even if pulsationsare attenuated during propagation to the extension chamber 704,variations of pressure in the compression chamber 706 neverthelessresult in overall pulsations in dP.

FIG. 19a depicts a system similar to that of FIG. 17a , except that thetype-1 accumulator 1701 has been substituted with a type-2 accumulator1901. As can be seen from FIG. 19b , merely substituting a type-1accumulator 1701 with a type-2 accumulator 1901 in a hydraulic systemhaving only a single accumulator only marginally improves attenuationcapacity. From this analysis, the inventors have recognized that even ifan accumulator is used to attenuate pulsations in one flow path of aclose coupled actuator system, or even if additional accumulators areadded to the flow path to further attenuate pulsations propagating alongthat flow path, such modifications are largely negligible with respectto overall pulsation performance if pulsations are free to propagate tothe actuator 700 through an alternative flow path (such as the flow pathfrom the pump to the opposing side of the actuator).

At least partly in view of the above, the inventors have recognized thata system incorporating two accumulators, as shown in FIG. 20a ,including an extension-side accumulator 2003 located in direct fluidcommunication with the extension flow path 716 and a compression-sideaccumulator 2001 located in direct fluid communication with thecompression flow path 724, may, exhibit pulsation attenuation capabilitythat greatly exceeds the individual contributions of either accumulatorconsidered alone. As can be observed by comparing FIG. 20b with FIGS.17b-19b , utilizing two accumulators—one in fluid communication with thecompression flow path coupling the pump to the compression chamber ofthe actuator and the other in fluid communication with the extensionflow path coupling the pump to the extension chamber of the actuator—maybe much more effective at attenuating pulsations in dP over a largerrange of frequencies (from at least as low as 30 Hz to at least above200 Hz). In this particular system, the two accumulators worksynergistically such that pulsations are attenuated in various flowpaths between the pump 718 and the actuator, resulting in greatlyattenuated pulsations in dP at lower frequencies. At the higherfrequencies the accumulators may lose effectiveness because the neck ofone or more accumulators may become blocked due the inertance of thefluid in the neck. Alternatively or additionally the magnification atthe higher frequencies may occur, for example, because of thesuperimposition or near superimposition of one or more resonancefrequencies of the system.

FIG. 21a depicts a system similar to FIG. 20a having two accumulatorslocated on either side of the pump to allow for the aforementionedsynergistic benefits, except that in FIG. 21a the compression-sideaccumulator 2101 is a type-2 accumulator. FIG. 21B describes thepulsation behavior of dP in response to ripple generated at the pump inthe system of FIG. 21a . As disclosed earlier, inventors have recognizedthat, for various reasons, in certain applications a type-2 accumulatorproperly configured and positioned in accordance with the teachingsherein may be more effective than type-1 accumulators. Indeed, as can beseen by comparing FIG. 21b , to FIG. 20b , utilization of a type-2compression-side accumulator results in substantially improved dPattenuation for pulsations having a frequency above approximately 70 Hzas compared to a similar system having a type-1 compression-sideaccumulator.

FIG. 22a illustrates a system in which both the extension-sideaccumulator 2103 and compression-side accumulator 2101 are type-2accumulators. As can be seen in FIG. 22b , pulsation attenuation ismarkedly improved by making each of the extension-side accumulator 2103and compression-side accumulator 2101 a type-2 accumulator.

In certain embodiments, therefore—especially embodiments forapplications in which pulsation attenuation is a priority—both of thecompression-side accumulator 2101 and extension-side accumulator 2103may be type-2 accumulators. However, as discussed previously, type-2accumulators require incorporation of additional flow paths havingassociated inertances and impedances, and may ultimately decreasecertain performance metrics, such as response time of the hydraulicsystem. Therefore, in alternative embodiments, only one of thecompression-side accumulator 2101 and extension-side accumulator 2103may be type-2, and the other accumulator may be a type-1 accumulator. Inyet alternative embodiment—for example, for embodiments designed forapplications in which response time is highly prioritized relative topulsation attenuation—both the extension-side accumulator 2103 andcompression-side accumulator 2101 may be type-1 accumulators. Further,the inventors again note that, as can be seen by comparison of FIG.17a-b and FIG. 19a-b , simply replacing a type-1 compression-sideaccumulator with a type-2 compression-side accumulator does notnecessarily result in substantial system improvement over a wide-rangeof frequencies. Rather, it is, in certain embodiments, the specificsynergy that results from having the two accumulators in the particularlocations described above, wherein at least one of the accumulators istype-2 accumulator, that allows for such improvement.

FIG. 24 demonstrates empirical results illustrating how inertance of thecompression-side first flow path 728 affects pulsation attenuation in asystem having a type-2 compression side accumulator 726 and a type-1extension-side accumulator 720, such as that illustrated in FIG. 8. Ascan be seen in FIG. 24, increasing inertance of the compression-sidefirst flow path 728 results in a decrease in the magnitude of forceripple resulting from displacement ripple at the pump; indeed, the trendis observed for pulsations at both 70 Hz and 250 Hz, being morepronounced at the latter frequency.

A person of ordinary skill in the art contemplating the presentdisclosure will readily appreciate that practical actuator embodimentsmay tend to include passageways and components that may be geometricallyand functionally complex while still adhering to the conceptualframework described herein. For example, FIGS. 25a-d illustrate apractical embodiment of a hydraulic system similar to that shownschematically in FIG. 11B. As can be seen in FIG. 25a , the illustratedembodiment comprises a housing 1110 that internally contains both a pump(not pictured), an extension-side accumulator (not pictured), and anextension-side first flow path (not pictured); an extension side secondflow path 701 fluidically coupling the extension-side accumulator to theextension chamber 704 of the actuator; a compression-side first flowpath that fluidically couples the pump contained in the housing 1110 toa compression-side accumulator 726; and a compression-side second flowpath 730 that fluidically couples the compression-side accumulator 726to the compression chamber 706 of the actuator. As illustrated, thecompression-side first flow path 728 includes both an annular cavityencircling at least a portion of the actuator housing as well as thebore of a first tube partially inserted into the housing of thecompression-side accumulator 726. As illustrated, the compression-sidesecond flow path 730 includes the bore of a second tube. Thecompression-side accumulator 726 is therefore similar to the type-2accumulator shown schematically in FIG. 12C. FIGS. 25b-d illustrateadditional views and/or portions of the practical embodiment shown inFIG. 25 a.

While complex three dimensional flow paths or distributedinertance/compliance can may have an effect, the teachings of thisdisclosure are believed to hold applicable across a range of suchvariations. For example, it is recognized that conveyance of fluid fromone point to another can proceed through multiple channels that may formcomplex parallel and series networks. As is the case in electricalcircuit theory as well as conventional fluid dynamics, insofar as agiven impedance exhibits an approximately linear response, complexnetworks can be roughly approximated as one single inertance. Applicantscertainly recognize that all fluid passages tend to exhibit non-linearimpedance behavior. While the analytical models discussed herein aregenerally approximated using linear elements, including linearinertances, these models can be extended to include non-linear effectsusing a combination of fluid mechanical principles, CFD tools, andempirical data.

As the term is used herein, a flow path is said to “fluidically couple”a first component to a second component when, under at least certainoperating conditions (e.g., certain pressures or certain configurationsof valves), fluid may flow from a chamber of the first component,through the flow path, to a chamber of the second component. If a flowpath comprises a switchable valve or other flow control device betweenthe first component and second component, the flow path is understood tofluidically couple the first component to the second component whetherthe valve is open or closed since, under at least certain operatingconditions (e.g., opening of the valve, increase in fluid pressure abovea pressure relief valve's set point, etc.), fluid may flow from achamber of the first component, through the flow path comprising thevalve, to the chamber of the second component. A flow path may comprisevarious pipes, tubes, nipples, bores, valves, open volumes, chambers, orother channels.

As used herein, a first component is said to be in “fluid communication”with a second component if a flow path exists that fluidically couplesthe first component to the second component that does not pass through apump.

As used herein, it is understood that the term “fluid,” unless contextindicates otherwise may encompass, for example, compressible andincompressible fluids and the term fluid communication may encompass,for example, hydraulic and pneumatic communication.

As used herein, the term compressible fluid is understood to mean gas orvapor.

As used herein, a “pump” is understood to mean a hydraulic device,component, unit or subunit that may be used, in at least one mode ofoperation, to receive fluid flow at one port at a first pressure and todeliver at least a portion of the flow at a second pressure, higher thanthe first, at a second port. A pump may use mechanical kinetic energy(e.g., rotation of a rotor) to produce a fluidic pressure difference. Insome embodiments, fluid delivered at the second higher pressure may flowto one or more other apparatus (e.g. an accumulator, an actuator, ahydraulic motor) by means of or through a flow path. In someembodiments, the pump may have a housing that includes a portion of theflow path between the pump and another hydraulic apparatus.

In certain embodiments, a pump may also be used to convert fluidicpressure difference into mechanical kinetic energy in a secondoperational mode. A pump may refer to a hydraulic pump or may refer to ahydraulic motor that may be operated as a hydraulic pump. The pump inany of the hydraulic systems described herein may be operatively coupledto a motor (not pictured), for example an electric motor, that iscontrolled by a motor controller (not pictured). The motor controllermay receive a command profile (e.g., from an external controller oruser) as described above, and may control the motor such that thehydraulic system operates according to the command profile.

As used herein, a “compression chamber” and “extension chamber” areunderstood to mean chambers within a housing of a hydraulic actuatorthat are separated from each other by a piston received in the housingof the actuator. A piston rod may be attached to the piston on a facethat is adjacent to (e.g., exposed to fluid in) the extension chamber.The volume of the compression chamber contracts upon compression of theactuator (e.g., when the length of the actuator is decreased), and thevolume of the extension chamber contracts upon extension of the actuator(e.g., when the length of the actuator is increased).

As used herein, an “electric motor” (sometimes referred to as simply a“motor”) is understood to mean an electromechanical device that iscapable of converting electrical energy into mechanical kinetic energy(e.g., rotation of a rotor). In certain embodiments, an electric motormay be capable of converting mechanical kinetic energy into electricalenergy in a second operational mode. A motor may refer to an electricmotor or may refer to an electric generator that may be operated as anelectric motor. A motor is said to be “operatively coupled” to a pumpwhen (i) appropriate rotation of a rotor of the motor results in arotation of one or more rotatable elements of the pump and/or (ii)appropriate rotation of a rotatable element of the pump results in arotation of the rotor of the motor.

As used herein, a “controller” is understood to mean one or moreintegrated circuits (such as, for example, a processor) along withassociated circuitry and/or software that determines, communicatesand/or applies an output signal to a target component based on one ormore input parameters. As used herein, a “motor controller” isunderstood to mean a controller capable of applying a modulable signalto an electric motor, wherein applying the signal to the motor resultsin (i) a torque being applied by the motor to a component operativelycoupled to the motor (e.g., a pump), and/or (ii) rotation of a rotor ofthe motor.

The invention claimed is:
 1. A hydraulic apparatus comprising: ahydraulic actuator comprising an actuator housing that at leastpartially defines a compression chamber and an extension chamber; apump; and a compression-side accumulator comprising: a compression-sideaccumulator housing defining a first internal volume that is divided, bya first barrier, into a first contained chamber and a first workingchamber, wherein: the first working chamber is fluidically coupled tothe pump by a compression-side first flow path having a first inertance;the first working chamber is fluidically coupled to the compressionchamber by a compression-side second flow path having a secondinertance; and the first inertance is larger than the second inertance.2. The hydraulic apparatus of claim 1, wherein a first TFmag of a firsttransfer function has at least one of a first global maximum or firstlocal maximum at a first frequency, and a second TFmag of a secondtransfer function has at least one of a second global maximum or secondlocal maximum at a second frequency, wherein: the second frequency ishigher than the first frequency; the first transfer function describes afirst relationship between pressure at a first point and pressure at asecond point; the second transfer function describes a secondrelationship between pressure at the second point and pressure at athird point; the first point is located in one of: the pump, a port ofthe pump, or the compression-side first flow path; the second point islocated in the first internal volume of the compression-sideaccumulator; and the third point is located in the compression chamberof the hydraulic actuator.
 3. The hydraulic apparatus of claim 2,wherein the second frequency is equal to at least 5 or at least 20 timesthe first frequency.
 4. The hydraulic apparatus of claim 3, wherein thesecond frequency is greater than the first frequency by a factor of lessthan
 100. 5. The hydraulic apparatus of claim 2, wherein the firstfrequency is higher than a first lower limit and lower than a firstupper limit, wherein the first lower limit is one of 0 Hz, 2 Hz, 5 Hz,or 10 Hz and the first upper limit is one of 100 Hz, 80 Hz, 60 Hz, 50Hz, 30 Hz, 20 Hz, or 15 Hz.
 6. The hydraulic apparatus of claim 2,wherein the second frequency is higher than a second lower limit andlower than a second upper limit, wherein the second lower limit is oneof 100 Hz, 200 Hz, 300 Hz, 400 Hz, or 500 Hz and the second upper limitis one of 800 Hz, 1000 Hz, or 1500 Hz.
 7. The hydraulic apparatus ofclaim 1, wherein a first TFph of a first transfer function is equal to+/−90° at a first frequency, and a second TFph of a second transferfunction is equal to +/−90° at a second frequency, wherein the firsttransfer function describes a first relationship between pressure at afirst point and pressure at a second point; the second transfer functiondescribes a second relationship between pressure at the second point andpressure at a third point; the first point is located in one of: thepump, a port of the pump, and the compression-side first flow path; thesecond point is located in the first internal volume of thecompression-side accumulator; and the third point is located in thecompression chamber of the hydraulic actuator.
 8. The hydraulicapparatus of claim 7, wherein the compression-side accumulator is atype-2 accumulator.
 9. The hydraulic apparatus of claim 7, furthercomprising: an extension flow path fluidically coupling the pump to theextension chamber; and an extension-side accumulator comprising: anextension-side accumulator housing defining a second internal volumethat is divided, by a second barrier, into a second contained chamberand a second working chamber, wherein: the second working chamber isfluidically coupled to the pump via an extension-side first flow path;and the second working chamber is fluidically coupled to the compressionchamber via an extension-side second flow path.
 10. The hydraulicapparatus of claim 1, wherein the compression-side accumulator is atype-2 accumulator.
 11. The hydraulic apparatus of claim 1, furthercomprising: an extension flow path fluidically coupling the pump to theextension chamber; and an extension-side accumulator comprising: anextension-side accumulator housing defining a second internal volumethat is divided, by a second barrier, into a second contained chamberand a second working chamber, wherein: the second working chamber isfluidically coupled to the pump via an extension-side first flow path;and the second working chamber is fluidically coupled to the compressionchamber via an extension-side second flow path.
 12. The hydraulicapparatus of claim 11, wherein the extension-side accumulator has asecond stiffness and the compression-side accumulator has a firststiffness, wherein the second stiffness is greater than the firststiffness.
 13. The hydraulic apparatus of claim 11, wherein theextension-side accumulator is a type-2 accumulator.
 14. The hydraulicapparatus of claim 13, wherein the compression-side accumulator is atype-2 accumulator.
 15. A hydraulic apparatus comprising: a hydraulicactuator comprising an actuator housing that at least partially definesa compression chamber of the hydraulic actuator and an extension chamberof the hydraulic actuator; a bi-directional pump; and a compression-sideaccumulator comprising: a compression-side accumulator housing defininga first internal volume that is divided, by a first barrier, into afirst contained chamber and a first working chamber, wherein the firstcontained chamber includes a compressible fluid, and wherein: the firstworking chamber is fluidically coupled to the bi-directional pump by acompression-side first flow path; the first working chamber isfluidically coupled to the compression chamber of the hydraulic actuatorby a compression-side second flow path; wherein the compression-sidefirst flow path is entirely distinct from the compression-side secondflow path, and wherein at least one of (a) or (b) is true; (a) a firstTFmag of a first transfer function has at least one of a first globalmaximum or first local maximum at a first frequency, and a second TFmagof a second transfer function has at least one of a second globalmaximum or second local maximum at a second frequency, wherein thesecond frequency is higher than the first frequency; (b) a first TFph ofthe first transfer function is equal to +/−90° at a first frequency, anda second TFph of a second transfer function is equal to +/−90° at asecond frequency, wherein the second frequency is higher than the firstfrequency and wherein: the first transfer function describes a firstrelationship between pressure at a first point and pressure at a secondpoint; the second transfer function describes a second relationshipbetween pressure at the second point and pressure at a third point; thefirst point is located in one of: the bi-directional pump, a port of thebi-directional pump, and the compression-side first flow path; thesecond point is located in the first internal volume of thecompression-side accumulator; and the third point is located in thecompression chamber of the hydraulic actuator.
 16. The hydraulicapparatus of claim 15, wherein (a) is true.
 17. The hydraulic apparatusof claim 15 wherein (b) is true.
 18. The hydraulic apparatus of claim15, wherein the second frequency is higher than the first frequency by afactor of at least
 5. 19. The hydraulic apparatus of claim 18, whereinthe compression-side accumulator is a type-2 accumulator.
 20. Thehydraulic apparatus of claim 15, wherein the first frequency is higherthan a first lower limit and lower than a first upper limit, wherein thefirst lower limit is one of 0 Hz, 2 Hz, 5 Hz, or 10 Hz and the firstupper limit is one of 100 Hz, 80 Hz, 60 Hz, 50 Hz, 30 Hz, 20 Hz, or 15Hz.
 21. The hydraulic apparatus of claim 15, wherein the secondfrequency is higher than a second lower limit and lower than a secondupper limit, wherein the second lower limit is one of 100 Hz, 200 Hz,300 Hz, 400 Hz, or 500 Hz and the second upper limit is one of 800 Hz,1000 Hz, or 1500 Hz.
 22. The hydraulic apparatus of claim 15, whereinthe compression-side first flow path is the shortest flow path of afirst set of one or more flow paths, and the compression-side secondflow path is the shortest flow path of a second set of one or more flowpaths, wherein: the first set of one or more flow paths consists of eachflow path of the hydraulic apparatus that fluidically couples thebi-directional pump to the first working chamber; and the second set ofone or more flow paths consists of each flow path of the hydraulicapparatus that fluidically couples the first working chamber to thecompression chamber.
 23. The hydraulic apparatus of claim 15, whereinthe compression-side accumulator is a type-2 accumulator.
 24. Thehydraulic apparatus of claim 15, wherein the compression-side first flowpath has a first inertance, the compression-side second flow path has asecond inertance, and wherein the first inertance is larger than thesecond inertance.